Prep Pan Preheat oven to 350°F. Line an extra large (18x14-inch) baking sheet with parchment paper.

Make Dough In a large bowl beat butter with a mixer on medium to high 30 seconds. Add both sugars, baking powder, and salt. Beat on medium until fluffy, scraping bowl as needed, about 2 minutes. Add egg whites, heavy cream, vanilla, and almond extract; beat until combined. Beat in flour just until combined.

Form Cookies Drop dough by ½ cup portions, 3 inches apart, onto prepared cookie sheet. Flatten mounds to ½-inch thick and 4-inches in diameter. Bake until edges are set (cookies will be pale), 13 to 14 minutes. Cool on cookie sheet 2 minutes. Remove; cool completely on wire racks. Repeat with remaining dough.

Frost Spread ⅓ cup Almond or Vanilla Buttercream Frosting on top of each cooled cookie.

Make Frosting In an extra-large bowl beat 1 cup softened salted butter with a mixer on medium to high, 1 to 2 minutes. Beat in 1 cup powdered sugar. Add 2 Tbsp. heavy cream, 1 tsp. almond extract, and a dash of salt; beat on low until combined. Gradually beat in 3 cups powdered sugar just until combined. Beat on medium until fluffy, scraping bowl occasionally, 5 minutes. Add 1 Tbsp. heavy cream; beat on high 1 minute more. (Makes 2 ¾ cups)

Make Frosting Follow the recipe for Almond Buttercream Frosting, but omit almond extract and use 1 tsp. vanilla extract.