01 - Preheat oven to 350°F. Grease and line a 9x13-inch baking pan with parchment paper.
02 - In a large bowl, whisk together melted butter, granulated sugar, and brown sugar until well combined. Add eggs one at a time, mixing well after each addition. Stir in vanilla extract.
03 - In a separate bowl, sift together flour, cocoa powder, baking powder, and salt.
04 - Gradually fold dry ingredients into wet mixture until just combined. Do not overmix.
05 - Pour batter into prepared pan and smooth the top with a spatula.
06 - Bake for 22 to 25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs. Cool completely in the pan.
07 - Beat softened butter until creamy. Gradually add powdered sugar, mixing on low speed. Add milk, vanilla extract, salt, and pink food coloring, then beat on high speed until fluffy and evenly colored.
08 - Once brownies have cooled, lift them out of the pan and place on a cutting board. Use a heart-shaped cookie cutter to cut out brownie hearts.
09 - Spread or pipe pink frosting on each heart-shaped brownie. Decorate with sprinkles if desired.