Preheat the oven to 375 °F (190 °C). Get out two cookie sheets, but don’t line them with parchment.
Whisk the egg yolk with the cream and the vanilla. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, cream the butter with the granulated sugar and the salt. Add the egg yolk mixture and beat it in. Add the flour and mix it in on low until combined.
Press the cookie dough together and fit it into the cookie press barrel, fitted with the Christmas tree stencil (or whichever you choose). I used this cookie press from Wilton available on Amazon.
Press out cookies onto ungreased, unlined sheets, spacing them about an inch apart. If you are decorating with coloured sugar, now is the time to do so!
Bake the cookies until the edges are light golden brown (about 12 minutes).
Let the sheet of cookies cool no more than 2 minutes before using an offset spatula to gently unstick the cookies from the sheet pan. You need to do this when the cookies have just set but before they cool down too much, otherwise they will break.
Cookie presses work best on ungreased sheet pans without lining them with parchment paper.
If you find your cookies spread too much in the oven and you are sure you didn't mismeasure the ingredients, try placing the sheet pan in the fridge for 15 minutes to chill the spritz cookies before baking them. This will reduce the spread. Don't chill the dough before pressing out the cookies because the dough will be too stiff and you may break your cookie press.
As soon as the cookies come out of the oven, when the cookies are still quite hot, use a mini offset spatula to unstick the cookies from the pan gently. They should come off without breaking.
If the cookies cool down and are stuck, you can try rewarming the sheet pan in the oven, and hopefully, when warm, the cookies will unstick more easily.
For almond spritz cookies, incorporate (0.625 mL) ⅛ teaspoon of almond extract in the cookie dough.
For chocolate spritz cookies, add 30 grams (⅓ cup) of Dutch-processed cocoa powder when you add the flour to make a chocolate spritz cookie dough.
To decorate spritz cookies, either garnish with sprinkles or sanding sugar before baking, or dip in melted chocolate after baking.
You can order the coloured decorative sanding sugar on Amazon.