In a large bowl or in the bowl of a stand mixer, beat the unsalted butter and sugar working your way up to high speed for 2 minutes.
3/4 cup unsalted butter, 1/2 cup sugar
Add the egg and vanilla extract, then beat on high speed for 1 minute.
1 egg, 2 tsp vanilla extract
Turn the mixer down to low and add the flour mixture. Mix until combined. The dough should be soft, but not too sticky to roll. Add a spoon of flour if necessary.
Divide the dough into two parts. Place each part on a piece of parchment paper or silicone baking mat. Top each with another piece of parchment paper or silicone baking mat. Roll out the dough to about 1/4-inch thickness.
Freeze for 20 minutes.
Using a 3-inch cookie cutter, cut the dough into circles and set on a baking sheet lined with parchment paper or a silicone baking mat.
When soft enough to form into the triangles, add 2 teaspoons of filling to the center of each circle.
Fold in the sides, slightly overlapping the filling, to form a triangle. Each side of the cookie should have a corner that folds under and another that folds over. (See photos in post.) Pinch the corners together neatly so that they form a point.
Freeze the cookies on the pans for 30 minutes. In the meantime, preheat the oven to 395F.
Bake for 10-12 minutes until just barely getting golden.
Cool on a wire rack completely before serving.
Notes
The dough can be frozen for up to 3 months. Shape them into discs about 1 inch thick, and seal in a sealable air-tight bag. Thaw until pliable, then continue with the recipe.This recipe only works with room temperature butter. Please do not use melted or firm butter.** Nutrition facts for this recipe are per cookie and do not include the filling.