How to cook
Prepare a rectangular oven dish to lay out with baking paper. The edges of the paper must go well beyond the walls of the dish, so that you can cover the entire cake's top with it later. Beat the eggs with the sugar and add both cocoa and sweetened condensed milk.
Pour the mixture in a container on the stove, in which you've slightly heated the butter. Stir the cream until it thickens over low heat. Add the vanilla and half the rum flavoring to the finished cream.
Pour the other half into a bowl with some milk, which you're going to use to gently dip one side of each biscuit. Place some of the cream into the bottom of an oven dish.
Arrange a row of biscuits dipped in milk and alternate between cream and biscuits, until you run out of products. You're going to get about 6 rows of biscuits. Be sure not to lay on the cream too thick.
Finish the top off with cream, leave it briefly to harden. Fold the baking paper over the top of the biscuit cake, to cover it completely.
Place in the refrigerator for 1 day and then serve it the next.