Preheat your oven to 350°F (175°C) and prepare 9-inch round cake pans by greasing them with unsalted butter and dusting with flour.

In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt until combined.

In a large mixing bowl, cream together butter and sugar until light and fluffy.

Add eggs one at a time, mixing well after each addition, followed by the vanilla extract.

Mix in the sour cream until fully blended.

Gradually combine the dry mixture with the wet ingredients, stirring gently until just incorporated.

Stir in hot water or brewed coffee until the batter is smooth.

Pour the batter into prepared pans and smooth the tops with a spatula.

Bake for 30-35 minutes, checking doneness with a toothpick.

Remove from oven and cool on a wire rack for about 10 minutes, then transfer cakes to cool completely.