Prep your pan: Heat the oven to 350°F (175°C). Grease and line an 8-inch round or 9-inch square pan with parchment. Lightly flour if you like extra insurance.
Mix dry ingredients: In a large bowl, whisk 1½ cups all-purpose flour, ½ cup unsweetened cocoa powder, 1 cup sugar, 1 teaspoon baking powder, ½ teaspoon baking soda, and ½ teaspoon fine salt until evenly combined.
Brew the hot liquid: Prepare ¾ cup hot coffee (or hot water).
Keep it hot; it helps bloom the cocoa.
Combine wet ingredients: In a measuring jug, whisk ½ cup neutral oil, ¾ cup buttermilk (or ¾ cup milk + 2 teaspoons lemon juice or vinegar, rested for 5 minutes), and 2 teaspoons vanilla extract.
Make the batter: Pour the wet mixture into the dry ingredients. Stir with a whisk until almost smooth. Gradually whisk in the hot coffee.
The batter will be thin—this is correct.
Optional boosters: Fold in ¼ cup mini chocolate chips or ¼ teaspoon espresso powder for extra intensity.
Bake: Pour the batter into the prepared pan. Bake for 28–35 minutes, or until a toothpick comes out with a few moist crumbs but no wet batter. Start checking at 27 minutes.
Cool: Let the cake cool in the pan for 10–15 minutes, then turn out onto a rack and cool completely before frosting.
Frost or finish: Spread with chocolate ganache or cocoa buttercream, or simply dust with powdered sugar.
Slice and enjoy.