With melted butter, grease a bundt cake mold or kouglof mold with a brush (mine is 1,5L but you can use a little larger). Sprinkle the inside of the mold with bitter cocoa and tap to remove the excess (this will give a shine to the cake).
In a food processor or mixer, beat the soft butter with the brown sugar and the whole grain sugar until very creamy, about 5 minutes.
Incorporate the vanilla then the eggs one by one, mixing between each. Finish with the cream.
Separately, mix the cocoa, flour, baking soda and salt.
Incorporate these dry ingredients in two batches into the dough, mixing just until necessary (do not overmix). It's thick and that's normal. Add hot water to the dough to obtain a smooth texture.
Pour the dough into the mold and bake for around 55 minutes: this varies a lot depending on your mold and your oven. You have to watch and stick a wooden pick in to see if it is cooked: it should come out with a few crumbs.
Leave to cool in the mold for 15 minutes then invert onto a rack to cool completely.
Chocolate ganache
Roughly chop the chocolate and place in a heat-resistant container.
In a small saucepan, heat the cream until lightly boiling. Then pour over the chocolate. Leave to rest for 1 minute then mix to obtain a smooth ganache.
Wait until the ganache takes on a consistency: neither too liquid nor too thick to be poured on top of the cake. You can speed it up by putting it in the refrigerator but be careful that it doesn't harden too much.
Pour the ganache with a tablespoon on top of the cake. Wait for the ganache to set a little (it will remain creamy). Add the small golden eggs in the center for decoration and enjoy!
PS: you will have enough ganache left to coat each part afterwards. You can reheat it for a few moments in the microwave to make it more liquid.
Notes
This Easter cake can be kept at room temperature (in an airtight container) for up to 3-4 days. It can also be placed in the refrigerator but be careful it will lose some of its softness...