I decided it was time to go back to basics with this rhubarb pie topped with a simple lattice crust. Rhubarb is rather deceptive: if you look at it and you cut into, it doesn't exactly seem like a juicy fruit, especially when compared to something like a plum or a peach.
Rhubarb actually does contain a lot of water (rhubarb is almost 94% water!), which means that as you bake your rhubarb pie, the cells will break down and the water will be forced out into your pie filling. All that extra water will make a very soupy rhubarb pie that is too liquidy, if you aren't careful. To avoid this, you have to use the right thickener.
Thickener for rhubarb pie: tapioca starch
Like with all pie fillings, you have many options to gel all that liquid and set the filling: flour, cornstarch, quick-cooking tapioca, and tapioca starch.
For rhubarb pie, I use tapioca starch as the thickener for the filling and I recommend to use a lot of it: ½ cup tapioca starch to gel 2 pounds of rhubarb. And though this seems like too much tapioca starch because it is a lot more thickener than you would use for, say, an apple pie, after letting the baked pie rest/gel overnight, the set of the pie is perfect. Soft, still a touch fluid, but not soupy at all.
This rhubarb pie filling was just right in my opinion, and it continued to thicken so that a full 24 hours after baking the pie, I found that a slice could be cut cleanly from the pie with zero leakage. Call me impressed! So this would mean that you need to use 30 grams (¼ cup) of tapioca starch to properly set every 450 grams (1 pound) of fresh rhubarb. That's the rhubarb pie filling ratio to keep in mind for future pies. It works!
In general, tapioca starch has a higher thickening power than flour, which means:
- use tapioca starch to thicken pies made with very wet fruit, like rhubarb, raspberries, blueberries, etc. For this kind of fruit, you will need a fair amount of starch (as in the recipe below)
- use tapioca starch if you want to achieve a clear set, but use sparingly for fruit that are less juicy, like in this wine-poached pear pie where I only used 1 tablespoon
- use flour as a thickener for an apple pie, like in this maple apple pie or this whiskey peach pie
- use eggs for a custard filling like in this beautiful, traditional maple syrup pie, apple butter pie, or pumpkin tarts where your filling is made from a liquid like maple syrup
Note that for crisps and crumbles, like this blueberry rhubarb crisp with oat crumble topping, I like to use less thickener because I prefer the fruit layer in these to be more "saucy" and less set.
Par-bake the rhubarb filling
For this rhubarb pie recipe, I used fresh rhubarb and, just like with many blueberry pie recipes, I cooked half the rhubarb to soften it and allow the juices to run, then mixed that soft rhubarb filling with more fresh rhubarb to make the ultimate rhubarb pie filling. This is a technique I picked up from Stella Parks.
Par-cooking the filling allows you to more evenly mix in the sugar which will dissolve with the sugar of the fruit and the thickener will begin to hydrate so that it gels more evenly. The goal is to avoid having a pie filling with clumps of sugar at the bottom or patches of starch.
I sweetened the filling with a mixture of granulated sugar and maple sugar (for some extra flavour) and I added a lot of vanilla, which really enhanced the filling. I also followed Stella Parks trick to add a little baking soda to the filling to reduce that astringent "spinach teeth" filling that rhubarb can leave behind. It certainly did not eliminate the issue, but I felt it was reduced. Definitely something to experiment with next time you make a rhubarb pie or a rhubarb crumble.
Easy food processor all-butter pie dough
After unsuccessfully trying other people's recipes for pie dough that have more butter to achieve a richer crust, more complicated folding techniques for better layering, and different rolling techniques, I decided to throw all those recipes out the window and to return to the pie dough that works for me. This pie dough might be less rich than some, and it's certainly not as flaky as a rough puff pastry, but you know what? This pie dough works well and is very easy to make and to use.
The dough is made in the food processor. It's extremely easy to roll and to work with, it keeps it's shape in the oven, it doesn't ooze butter as it bakes... Screw all the other recipes. This is still my go-to crust. I like it. It works well. It's forgiving. Most importantly, after hours of pie-making work, this dough doesn't leave me feeling like the worst baker on the planet like some of the others that have complicated my life over the years.
Video demo of how to make a lattice crust
This rhubarb pie with a lattice crust is one of the best pies I've made in a long time and one of the best rhubarb recipes on the blog. I'm hoping this double crust rhubarb pie is the first of many great pies to come. What pie should I made next?
By the way, if pie seems like too much effort, try this fantastic blueberry rhubarb crisp, this rhubarb bostock recipe, or these honey-sweetened strawberry rhubarb crumbles, which are much faster to make and easier too! You can always make rhubarb jam without pectin, if you can't be bothered with any of the more elaborate recipes.
Freezing instructions for rhubarb pie
Please note that if you want to freeze this pie, you should do so BEFORE baking. Here are the steps for freezing this pie
- make the filling and the dough, assemble the pie as if you were going to bake it today
- freeze the unbaked assembled pie completely for about 1 hour until it's frozen solid
- wrap the frozen rhubarb pie in plastic wrap tightly. Use several layers
- wrap in aluminum foil and label the pie with what it is and today's date
- store in freezer
To bake the frozen pie
You can bake the pie from frozen but it will take ages to properly bake the crust and get the filling to heat through and come to a boil in the middle. For this reason, I recommend defrosting the pie in the refrigerator overnight before baking.
To store the baked pie
I prefer to store this pie at room temperature, wrapped with aluminum foil. I don't think it's necessary to store it in the fridge, but if it's very hot where you live, you might want to consider refrigerating the baked pie in that case.
The best rhubarb pie with lattice crust
Rhubarb pie filling thickened with tapioca starch
Easy all-butter pie dough made in food processor
- 312 grams (2 ½ cups) all-purpose flour
- 1 tbsp (1 tbsp) granulated sugar
- 1 tsp (1 tsp) Diamond Crystal fine kosher salt
- 173 grams (¾ cup) unsalted butter cut into cubes, very cold
- 100 mL (7 tbsp) water
- 1 tbsp (1 tbsp) milk (2 % fat)
- 1 tbsp (1 tbsp) Turbinado sugar
Start by making the rhubarb pie filling
- Preheat the oven to 400ºF.
- Slice the rhubarb into ½-inch to 1-inch chunks. Place half of the chopped rhubarb into a 8x8 non-reactive glass baking (I used a Pyrex baking dish you can find on Amazon). Mix it with the granulated sugar, maple sugar, tapioca flour, and salt. Cover tightly with aluminum foil. Bake for 30 minutes or until the fruit is soft and the juices have run.
- Remove from the oven and add baking soda. Mix well. Add the rest of the rhubarb and the vanilla, stir, and transfer to a bowl then place in freezer to chill.
Meanwhile, make the easy all-butter pie dough in the food processor
- In the bowl of a food processor fitted with the metal blade, combine the flour, sugar, and salt. Add the cold butter and pulse to form a coarse crumble.Add the water and pulse it in, then let the food processor run just until the dough comes together. I bought my Cuisinart Food Processor on Amazon.
- Divide the dough in two and transfer both pieces to your work surface. Shape one piece into a disk. Shape the other into a rectangle. Wrap both in plastic wrap and chill for 1 hour.
- After 45 minutes of chilling. Retrieve the rectangle of dough. Roll it to a 10x15 rectangle on a floured surface. Transfer to a big cookie sheet and chill again.
- Roll the disk to a 14" circle. Transfer to metal pie plate and fit it in place. Pour the chilled filling into the pie and smooth it so it's even. Place in the fridge.
- Retrieve the big 10x15 rectangle of dough. Cut it into at least 12 one-inch strips. Take the pie out of the fridge and place 6 strips side by side vertically.
- Now weave in the other 6 strips horizontally to form a lattice (check out the video). Trim and crimp the edges.
- Chill the pie in the fridge for 45 minutes. Meanwhile place a large cookie sheet on the bottom rack of the oven. You will bake the pie on this sheet so make sure there's enough headspace for a pie!
- When the pie has chilled, brush the surface of the lattice with milk and sprinkle with turbinado. Bake the pie on the bottom rack on the preheated cookie sheet for 30 minutes at 400ºF. Lower the oven temperature to 350ºF and continue baking until the edges and top of the pie crust are golden brown. The filling should be bubbling and very hot. This takes at least 50–60 minutes more of baking.
- Let the pie cool to room temperature, preferably overnight (even 24 hours) so that the pie sets properly before serving.