In a separate bowl, mix the sifted flour, cocoa and baking powder.
Beat in a fluffy light mass of eggs, sugar and a pinch of salt. Then, in several steps, mix the flour mixture with a spatula. Pour in the mixture of milk, butter and boiled condensed milk and mix everything carefully.
Pour the dough into a baking dish and place in a preheated 170-175°C oven for about 50 minutes. Check readiness with a skewer.
Ready sponge cake to cool on the grill.