Preheat the oven to 350°F (180°) and line a baking sheet with parchment paper. You may need two baking sheets.
Add the butter and sugar to a large mixing bowl. Use electric beaters to cream until fluffy, 1-2 minutes.
½ cup plus 2 tablespoons salted butter, ¾ cup sugar
Add the egg, vanilla, and almond extract. Beat for 1 minute to combine.
1 large egg, 1 teaspoon vanilla, ⅙ teaspoon almond extract
Add the flour, cornstarch, baking powder, and salt. Mix on low speed until just combined. The dough will look crumbly.
1 ¾ cup flour, 1 tablespoon cornstarch, 1 teaspoon baking powder, ¼ teaspoon salt
Use your hands to roll the dough into balls 1 tablespoon in size. Place the balls onto the prepared baking sheet, leaving about 1.5 inches (4 cm) between each ball.
Flatten the cookies with the palm of you hand to about ½ inch (1.2 cm) thick.
Bake for 8-10 minutes. The cookies shouldn't brown, so keep an eye on the time.
Cool the cookies on the baking sheet for 5 minutes before carefully transferring to a wire rack to cool fully. Once cool, top with buttercream and sprinkles.