Dark Chocolate Mousse Cake
c1 and 3/4 cups (220g) all-purpose flour (spoon & leveled) 3/4 cup (65g) unsweetened natural cocoa powder* (see note) 1 and 3/4 cups (350g) granulated sugar 2 teaspoons baking soda 1 teaspoon baking powder 1 teaspoon salt 2 teaspoons espresso powder (optional)* 1/2 cup (120ml) canola or vegetable oil 2 large eggs, at room temperature 3/4 cup (180g) full fat sour cream, at room temperature 1/2 cup (120ml) buttermilk, at room temperature* 2 teaspoons pure vanilla extract