Cream the butter and brown sugar in a large mixing bowl until light and fluffy.

Add the flour to the bowl and mix until combined on low speed with an electric or hand mixer. The dough will be crumbly, but that's okay. Use your hands to bring the dough together into a ball. If the dough is too crumbly, add a tablespoon of milk to help it come together.

Wrap the dough in plastic wrap and chill in the refrigerator for at least 30 minutes.

Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper. Use a cookie scoop or spoon to portion the dough into two big pieces and roll it into 2 balls. Flatten each ball slightly with a hand, a fork, or the bottom of a glass. Use a cookie cutter to create cookie shapes. Cut shapes closely together to prevent extra scraps and re-rolling. (If you don't have a cookie cutter, you can also use a fork to press down for a criss-cross pattern.) The bake time varies. Bake the cookies for 15 minutes or until the edges turn golden brown.

Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely.

Serve and enjoy your delicious 3-ingredient brown sugar cookies!