Preheat oven to 350°F (180°C). Spray an 8-inch round cake pan with baking spray with flour; line bottom of pan with parchment paper. 2. In a large bowl, whisk together flour, sugar, baking soda, and salt.

In a medium bowl, whisk together hot coffee or hot water and cocoa until smooth and well combined. Whisk in sour cream, oil, and vanilla until well combined. Whisk in egg until smooth. Whisk cocoa mixture into flour mixture just until no white streaks remain. Spread batter into prepared pan.

Bake until a wooden pick inserted in center comes out with a few moist crumbs, 30 to

35 minutes. Let cool in pan for 10 minutes. Remove from pan, and let cool completely on a wire rack.

Spread Chocolate Buttercream onto cooled cake. Garnish with chocolate, if desired. Store in an airtight container for up to 3 days.