Preheat oven to 350°F. Line a light colored baking sheets with parchment paper.
In a large bowl or in the bowl of your stand mixer beat slightly firm butter and sugar for 2–3 minutes until smooth and slightly pale (not airy).
1 & 1/4 cup butter, 1 cup granulated sugar
Mix in salt, vanilla extract, vanilla bean paste, almond extract (if using), 1 whole egg + 1 yolk, and milk until just combined.
3/4 tsp salt, 1 tbsp vanilla extract, 1 tsp vanilla bean paste, 1/2 tsp almond extract, 1 egg, 1 tbsp milk, 1 egg yolk
In a separate bowl, whisk flour, cornstarch, baking powder, and powdered milk. Gradually mix into wet ingredients on low speed until dough just comes together. Dough should hold together and not be sticky.
4 cups flour, 1 tsp corn starch, 1/8 tsp baking powder, 2 tsp powdered milk
Roll dough on lightly floured surface to about ⅓ inch (8 mm) thick. Cut shapes and transfer to prepared trays.
You can bake immediately for slightly softer edges, or chill 15–30 minutes in the freezer for sharper, cleaner shapes.
Bake 8–9 minutes until edges are lightly golden and bottoms just set. Avoid overbaking.