Preheat the oven to 175°C (350°F) and prepare a sheet cake pan with grease and parchment paper.
Mix flour, cocoa powder, baking powder, and salt in a bowl.
Beat sugar, butter, eggs, vanilla extract, and red food coloring until smooth.
Add buttermilk and dry ingredients gradually, mixing until a soft batter forms.
Pour the batter into the prepared sheet pan and bake for 25–35 minutes until a toothpick comes out clean.
Cool the cake completely before spreading cream cheese frosting.
Slice into squares and serve chilled or at room temperature.