Make the ganache ahead of time so it can harden. Heat the cream in the microwave and add the chocolate to it. Leave it for a few min., then stir to obtain a homogeneous mixture. Leave to cool completely and put in the fridge to harden.
Mix the eggs with the sugar and beat with a mixer for a few min. Add the soft butter, then the cocoa and continue beating. Add the flour with the baking soda, then the milk as well.
Beat until homogeneous, then divide the mixture into 2 medium-sized trays. Bake them in a preheated 374°F (190 °C) oven for about 30 min. until ready.
If the ganache has hardened well, set aside 1/2 of it for the glaze, beat the other 1/2 to a fluffy cream with a mixer. Once you've taken the layers out, wait for them to cool completely.
Smear 1 layer with the cream, place the 2nd layer on top and smear with the unbeaten ganache.