Preheat the oven at 170ºC/340ºF conventional oven and line a 20x20 cm/8x8 inch baking pan with parchment paper.
Start by making the coffee and weigh it out so it can cool down a bit while preparing the other ingredients.
180 g warm coffee or water
In a bowl, sift all of the dry ingredients together. Give it a stir to make sure everything has been combined.
180 g all-purpose flour, 1 tablespoon cornstarch, 150 g granulated sugar, 75 g dark brown sugar, 35 g unsweetened cocoa powder, ¾ teaspoon baking powder, ¾ teaspoon baking soda, ¾ teaspoon salt
In another mixing bowl add all of the wet ingredients, including coffee, and with a hand whisk, whisk them together until combined. Be sure to not mix the ingredients too vigorously so the eggs don’t get over mixed.
80 g vegetable oil, 135 g sour cream, 2 large eggs, 2 teaspoon vanilla extract
Slowly pour the wet ingredients into the dry while gently stirring it all together. Make sure there are no lumps left in the batter.
Pour the cake batter into the prepared baking pan and bake it for 35-40 minutes or until a cake tester comes out clean.
Let the cake cool on a wire rack. After 10 minutes, gently remove the cake from the baking pan and let the cake cool down completely.