Instructions for Gluten-Free Chocolate Sponge Cake:

Preheat the Oven: Preheat your oven to 355°F (180°C). Line two 7-inch round cake pans with greaseproof or baking paper.

Mix Dry Ingredients: In a large bowl, sift together the gluten-free flour, xanthan gum, baking powder, baking soda, and cocoa powder. Add the granulated sugar and salt, then whisk thoroughly to combine.

Add Wet Ingredients: Add the eggs, milk, and vegetable or sunflower oil to the dry ingredients. Whisk well until the mixture becomes a smooth cake batter.

Incorporate Boiling Water: Gradually add the boiling hot water to the batter, whisking continuously until the batter is runny and free of lumps.

Bake: Divide the batter evenly between the two prepared cake pans. Bake in the preheated oven at 355°F (180°C) for about 40 minutes, or until the sponges are springy to the touch and a toothpick inserted into the center comes out clean.

Cool: Allow the cakes to cool completely in the pans before removing.

Instructions for Chocolate Buttercream Frosting:

Beat the Butter: In a stand mixer or using a hand mixer with double beater attachments, beat the softened butter for 2–3 minutes until pale and fluffy.

Add Powdered Sugar: Gradually add the powdered sugar and beat for an additional 5 minutes until light and creamy.

Incorporate Cocoa and Salt: Add the cocoa powder and a pinch of salt, then beat until evenly distributed.

Add Melted Chocolate: Pour in the melted and cooled dark chocolate, and beat until the frosting is rich, fluffy, and has an even chocolate brown color.

Assembling the Cake:

Level the Sponges: If the cake layers have domed tops, use a serrated knife to level them.

Layer the Cake: Place the bottom sponge layer on a cake stand. Spread a generous layer of frosting on top, reserving enough for the outside of the cake. Place the second sponge layer on top.

Frost the Cake: Use the remaining frosting to cover the outside of the cake. Decorate by creating swirls with an offset spatula or the back of a spoon.