Preheat oven to 375°F and line a baking sheet with parchment paper or a silicone baking mat.
In a large mixing bowl, beat together ½ cup room-temperature butter and ¾ cup sugar until light and fluffy, about 2 minutes.
Add 1 large room-temperature egg and mix until fully combined.
Mix in 1 teaspoon vanilla extract and ½ teaspoon almond extract until incorporated.
In a separate bowl, whisk together 1½ cups flour, 2 teaspoons cornstarch, 1½ teaspoons baking powder, and ¼ teaspoon salt.
Gradually add the dry mixture into the wet ingredients, mixing until a stiff dough forms.
Stir in ½ cup rainbow jimmie sprinkles, being careful not to overmix.
Scoop dough and roll into 1-inch balls, then roll each ball in additional sprinkles if desired.
Place cookie dough balls on the prepared baking sheet.
Bake for 8–10 minutes for softer cookies or 11–12 minutes for crisp cookies.
Allow cookies to cool on a wire rack before storing in an airtight container.