Preheat the oven to 180ºC with heat up and down. Line with non-stick paper a rectangular mold of about 22-25 cm long. If it is smaller, the cake will come out higher; if it is longer, it will be shorter.
Chop the butter and the chocolate, and melt together in a bain-marie or directly in a saucepan, over very low heat. Stir until you have a homogeneous mixture and mix with the cocoa, stirring with the rods. Cool slightly.
Beat the eggs in a medium bowl with the sugar, several minutes until double or triple the volume. Add the milk and vanilla and beat a little more. Incorporate the melted chocolate mixture, stirring gently.
Sift the flour with the almonds, salt and yeast on top. Mix everything well, with gentle movements, and take to the mold when it is well homogeneous. Bake for about 35-40 minutes, ensuring that it does not pass.
It is better than poking the center with a toothpick come out a bit stained. Remove from the oven and wait 8-10 minutes before unmolding and letting cool completely on a wire rack.