Pink Grapefruit Sugar Cookies

Preparation

1. Cookies

   Step 1

   Place racks in upper and lower thirds of oven; preheat to 350°. Whisk together flour, cornstarch, baking powder, baking soda, and salt in a medium bowl.

   Step 2

   Using an electric mixer on medium speed, beat grapefruit zest, sugar, and butter in a large bowl until light and fluffy, about 3 minutes. Add egg, sour cream, and vanilla and beat to incorporate, about 2 minutes (the mixture might look curdled, and that’s okay). Reduce speed to low and beat in dry ingredients until just combined.

   Step 3

   Using a #30 cookie scoop (about 2 Tbsp.) and working one at a time, scoop out portions of dough and roll into balls (you should have about 24). Divide between 2 parchment-lined baking sheets, spacing at least 3" apart. Gently flatten cookies to about 1½" in diameter.

   Step 4

   Bake cookies, rotating baking sheets top to bottom and front to back halfway though, until edges are light golden but tops are still pale, 11–13 minutes. Let cookies cool 5 minutes on baking sheets, then transfer to a wire rack and let cool completely.

   Do Ahead: Cookies can be baked 5 days ahead; store airtight at room temperature.

2. Frosting and Assembly

   Step 5

   Using an electric mixer on low speed, beat powdered sugar, cream, butter, grapefruit zest, vanilla, and salt in a large bowl until combined. Increase speed to high and beat until light and fluffy, about 3 minutes. Using a toothpick or skewer, add a small drop of food coloring to frosting, then beat to combine.

   Step 6

   Spoon 1 heaping Tbsp. frosting onto each cookie; use a spoon or offset spatula to create swirls. Decorate cookies with sprinkles.

   Do aAhead: Cookies can be frosted and decorated 2 days ahead. Store airtight at room temperature.