If you want to make a simple sponge cake at home for Valentine's Day, sift flour, cocoa powder, baking powder, and baking soda in a bowl for a basic cake. In another bowl, whisk sugar and butter well. Add milk and vanilla essence. You can also add a little fresh yogurt to help the cake rise well. Now, mix all the dry ingredients well, preheat the oven to 180 degrees Celsius, and bake the cake for 30 to 35 minutes. Then, decorate it with your favorite ganache or frosting to make a decorative cake.