Sift together all dry ingredients in a bowl.
In another bowl, whisk together all wet ingredients and let sit for 10 minutes. (You can replace the eggs with 4 tbsp of thick yogurt.)
Mix the wet and dry ingredients together and pour into baking paper-lined cake tins. (Use 2x 6-inch cake tins to get two layers.)
Bake in a 170°C preheated oven for 20–25 minutes until a toothpick inserted in the centre comes out clean.
Let cool completely outside, then refrigerate.
Combine milk, cream, sugar, and cornstarch in a saucepan and whisk until no lumps remain. (You can add 1 tsp coffee powder to improve the flavour.)
Turn on the heat and cook on simmering gas until slightly thick — the texture of fresh cream.
Add chopped chocolate and whisk until fully melted.
Immediately turn off the gas, add salt, and whisk again.
Transfer cremeux to a bowl and cover with cling film.
Slice your cakes in half to get 4 layers. Pipe cremeux frosting in between and cover the outside with the frosting as well. Slice and serve.