Preheat the oven to 350°F (175°C). Grease a 9-inch round cake pan and line the bottom with parchment paper.
In a large mixing bowl, sift together the powdered sugar, cocoa powder, baking soda, and salt until well combined.
In another bowl, whisk together the melted butter, eggs, vanilla extract, red food coloring, and buttermilk until smooth.
Gradually add the wet ingredients to the dry ingredients, stirring until just combined. Do not overmix.
Pour the batter into the prepared cake pan and smooth the top with a spatula.
Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes, then carefully invert it onto a wire rack to cool completely.
Once cooled, dust with additional powdered sugar or top with cream cheese frosting if desired.