Prep the pan: Heat your oven to 350°F (175°C). Grease an 8-inch or 9-inch round cake pan and line the bottom with parchment for easy release.
Whisk dry ingredients: In a large bowl, whisk 1½ cups flour, 1 cup sugar, ½ cup cocoa powder, 1 teaspoon baking soda, ½ teaspoon baking powder, and ½ teaspoon salt until no streaks remain.
Mix wet ingredients: In a separate bowl or large measuring cup, whisk 1 cup non-dairy milk, ⅓ cup oil, 1 tablespoon vinegar, and 2 teaspoons vanilla.
Combine: Pour the wet mixture into the dry.
Whisk just until mostly smooth. It’s fine if a few small lumps remain.
Add hot liquid: Carefully pour in ½ cup hot coffee (or hot water). Stir gently until fully combined.
The batter will be thin—this is right.
Optional mix-ins: Fold in up to ½ cup dairy-free chocolate chips or other add-ins if using.
Bake: Pour the batter into the prepared pan. Bake for 28–34 minutes, or until a toothpick comes out with a few moist crumbs and the center springs back.
Cool: Let the cake cool in the pan for 10 minutes, then turn it out onto a rack, peel off parchment, and cool completely before frosting.
Frost (optional): Make a simple vegan chocolate buttercream by beating ½ cup vegan butter until fluffy, then mixing in 2 cups powdered sugar, ¼ cup cocoa, 1–2 tablespoons non-dairy milk, and 1 teaspoon vanilla until smooth. Spread over the cooled cake.
Serve: Slice and enjoy.
A sprinkle of flaky salt or fresh berries makes a nice finish.