01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
03 - In a large bowl, beat butter and sugar with an electric mixer until light and fluffy, about 2–3 minutes.
04 - Add the egg and vanilla extract; mix until well combined.
05 - Mix in red food coloring and vinegar until evenly distributed.
06 - Add half the dry ingredients, mixing gently. Pour in the buttermilk, then add remaining dry ingredients. Mix until just combined; do not overmix.
07 - Drop tablespoon-sized mounds of batter onto prepared baking sheets, spacing 2 inches apart.
08 - Bake for 10–12 minutes, or until cookies are set and spring back lightly when touched. Cool completely on wire racks.
09 - Beat cream cheese and butter together until smooth and creamy. Gradually add powdered sugar and vanilla, beating until fluffy.
10 - Pair cookies of similar size. Spread or pipe about 1 tablespoon of filling onto the flat side of one cookie; top with another cookie to make a sandwich. Repeat with remaining cookies and filling.