Start by preheating your oven to 350°F. Line your muffin pan with paper liners to get ready for the batter.
Mix the dry ingredients. In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, and salt.
Combine the wet ingredients. In another bowl, whisk buttermilk, oil, egg, and vanilla until smooth.
Bring the batter together. Pour the wet mix into the dry ingredients, whisking until just combined and smooth.
Fill the liners. Divide the batter evenly among the liners, filling each about two-thirds full.
Bake the cupcakes for 20 minutes, or until a toothpick comes out clean. Cool in the pan for a few minutes, then transfer to a wire rack.