These soft, sweet, and buttery shortbread cookies only require 4 ingredients! BONUS: the cookie dough is easy to make days or even weeks ahead of time until you're ready to bake!
Beat the butter and sugar in a large bowl with an electric mixer until fluffy. Stir in the vanilla and flour and mix until well-combined.
Roll the dough to 1/2 inch thick and use a cookie cutter to create the shapes (I used a round, 3-inch wide cutter).
Place the cookies on parchment paper-lined baking sheets and chill in the fridge for 30 minutes. (It's much easier to chill them after you've cut them, vs. rolling out chilled dough.)
Preheat oven to 350 degrees.
Bake the cookies for 12-18 minutes, (set the timer for 10 minutes and check them every 2 minutes after that)- they're done when they just begin to get golden brown on the side.
If adding sprinkles, brush just enough milk on each cookie to get it slightly wet on the top, then scatter the sprinkles over it. The milk helps them to stick. Let them cool slightly to prevent the sprinkles from bleeding onto the cookie.