2 cups all-purpose flour
2 tablespoons cocoa powder
1/2 teaspoon baking powder
1/4 teaspoon salt
1/2 cup (1 stick) unsalted butter, at room temperature
1 cup light brown sugar, packed
1 large egg
1 teaspoon vanilla extract
1/2 cup buttermilk, at room temperature
1 ounce red food coloring
8 ounces cream cheese, room temperature
5 tablespoons unsalted butter, at room temperature
2 teaspoons vanilla extract
2 and 1/2 cup confectioners' sugar, sifted
Preheat oven to 375 degrees. Using a heart template cut out from cardstock, or a cookie cutter, trace evenly spaced hearts onto pieces of parchment paper sized to fit two cookie sheets. Place the parchment on cookie sheets so that the side you have drawn on is facing down; set aside.
In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt. In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and brown sugar on medium-high until light and fluffy, about 2 minutes. Beat in the egg until incorporated, scraping down the sides of the bowl as necessary. Blend in the vanilla. With the mixer on low speed, beat in about a third of the dry ingredients, followed by half of the buttermilk, beating in each addition until just incorporated. Repeat with another third of the dry ingredients, remaining buttermilk, and finishing with dry ingredients. Do not overmix. Blend in food coloring.
Transfer batter to a pastry bag fitted with a large round tip, or a zip-top bag with the corner cut off works fine too. Pipe the batter onto the parchment paper using the heart tracings as a guide. Bake 7-9 minutes or until the tops are set, rotating the sheets halfway through. Allow the cookies to cool on baking sheets at least 10 minutes, until they can easily transfer to a cooling rack. Allow cookies to cool completely before filling.
To make the filling: In the bowl of a stand mixer fitted with the paddle attachment, beat the cream cheese and butter on medium-high until well combined and smooth, about 2-3 minutes. Mix in the vanilla extract. Gradually beat in the confectioners' sugar until totally incorporated, increase the speed and beat until smooth.
Using another pastry bag with a plain tip, or a zip-top bag with the corner cut off, pipe the cream cheese filling on the bottom side of one cookie and sandwich with another cookie (it helps if you pair up the similar matches to each cookie first).