In a large mixing bowl, beat the softened butter and powdered sugar together with an electric mixer for 3-4 minutes until light and fluffy. This step is key for creating the signature airy texture of this whipped shortbread recipe, so don't rush it! Add your choice of extract (vanilla, lemon, or orange) and mix to combine.

Sift the flour and cornstarch together, then gradually add them to the butter mixture. Beat on low speed just until the dough comes together. Don't overmix.

Scoop out about 1 tablespoon of dough for each cookie and roll it into a ball. You should get about 36 cookies. Place the dough balls on a baking sheet lined with parchment paper (or a floured plate to prevent sticking). Gently press each ball with a fork dipped in cornstarch or flour, then top with sprinkles, if using.

Transfer the tray or plate of dough balls to the refrigerator and chill for at least 2 hours, or until they are firm to the touch. (If you're in a hurry, you can speed this up by placing them in the freezer.)

While the dough chills, preheat your oven to 300°F (150°C).

Once chilled, place the dough balls on a cookie sheet and bake in the preheated oven for 19-20 minutes, or until the tops of the cookies are set but not browned.

Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.