Make the Spongecake
You will need: 5 tablespoons butter/ 2/3 cup cake flour/ 1/3 cup cocoa powder/ 1/8 teaspoon baking soda/ 6 eggs/ 3/4 cup sugar/ 2 teaspoons vanilla. Preheat oven to 350 degrees. Butter a quarter sheet baking pan and line with parchment paper. Butter and flour parchment paper and pan, removing any excess flour. Set aside. Sift flour, cocoa and soda together and whisk to ensure that it is well combined. Set aside. Clarify butter by melting over low heat and skimming off any milk solids on the top. Pour amber liquid into a small bowl and keep warm until ready to use.