• Prepare a 9x13-inch (23x33-cm) baking pan by buttering and lining the inside with a large sheet of parchment paper. Set aside.
• Prepare a large bowl or a Cambro, spraying it lightly with cooking spray or brushing a thin layer of neutral oil (like canola) all over the inside. Set aside.

To make the dough

• Whisk together the flour and salt in a medium bowl. Set aside for later.
• In the bowl of a stand mixer fitted with the paddle attachment, combine the warm milk, eggs, 70 grams (⅓ cup) sugar, and instant yeast. Stir them together for a few seconds on low just to get everything evenly mixed and to break up the eggs.
• Add the dry ingredients to the mixer bowl and stir everything together on low speed to form a shaggy, evenly mixed dough.
• Switch to the hook attachment and knead the dough for 5 minutes until it's smooth and elastic dough. The bowl will be clean.
• With the mixer kneading on low, add the butter, a little bit at a time. Note the dough will become rough and sticky with the fat of the butter interfering with the gluten temporarily.
• Knead the dough for 10 minutes in the mixer. You should end up with a smooth round ball of dough. The bowl will be clean again.
• Transfer the dough to the greased Cambro, cover with a towel, plastic wrap, or a shower cap, and let it rise until doubled in size (for about 45 minutes to an hour).

To make the filling

• In a bowl, cream together the softened butter, the sugars, and the cinnamon until you have a thick brown paste. Set aside.

Assemble the rolls

• When the dough has risen, remove the towel. Lightly flour your counter and transfer the dough to roll it out into a big rectangle of at least 12-x16-inches (30.5-x40.6-cm). Don't worry too much if it's a little bigger.
• Spread the filling over the entire surface of the dough, then roll neatly into a long 12-inch (30.5 cm) log.
• Cut the dough into 12 equal buns (you don't have to trim the ends much, if at all) and place them in the prepared baking pan. Cover with plastic wrap or a towel.
• Let the rolls rise until they have puffed and until proofed (if you lightly press your finger into the side of a roll, the indent should very slowly fill out and disappear).
• Meanwhile, preheat the oven to 350 °F (175 °C).
• Bake the buns until golden brown. This takes about 30 minutes. The internal temperature should be at least 190 °F (88 °C)—use an instant-read thermometer for this.
• Let the buns cool in the pan for 45 minutes to an hour before garnishing.

Topping the buns

• Dollop a spoonful of maple butter on each bun and use an offset spatula (or the back of a spoon) to spread it on top. Sprinkle with maple flakes. These are best served the day they are baked.