Step 1: Preheat the oven to 350F. Beat the egg yolks, sugar until they turns smooth and plate,add the flour,butter and chocolate powder to them, mix everything well and keep aside.
Step 2: Now whisk the egg whites with a pinch of salt until soft peeks forms. Fold the whipped egg whites to the already prepared chocolate batter, mix gently until they get well mixed.
Step 3: Line a baking sheet over a swiss roll pan or a baking tray,spread this batter and bake for 12minutes,until the top turns firm, remove the baking sheet carefully.
Step 4: Keep aside and let the sponge cake gets cooled. Now spread the already prepared chocolate mousse, roll them, arrange them in fridge for few hours and enjoy them.