Arrange the warm water in a medium bowl and dissolve the honey. Add the yeast, stir and add the buckwheat flour. Mix well, cover and let stand an hour or until it has grown in volume and is bubbly. Remove the eggs so they are not cold from the fridge.

Preheat the oven to 175ºC without air (slightly less if it is a very powerful oven) and grease or line a removable round mold of about 20-22 cm in diameter. Chop the butter and the chocolate, and melt together in a bain-marie.

Separate the yolks from the egg whites. Add the cocoa and vanilla to the melted chocolate and add the yolks and 25 g of sugar. Mix a little and add the flour and yeast sponge; combine gently until smooth.

Beat the remaining sugar (50 g) with the whites at high speed for about 4 minutes. Incorporate these whipped whites into the main dough in several batches, using a spatula with enveloping movements, until you have a homogeneous spongy dough.

Cake Baker Steps

Fill the mold and bake at medium height for about 40-45 minutes, turning the mold halfway through cooking to make it more homogeneous. Check the point towards the end with a toothpick to avoid overdoing it.

Allow to cool out of the oven, on a wire rack, for at least 20-30 minutes before carefully unmolding, and allow to cool completely before decorating with sifted icing sugar or cocoa, if desired.