Turn the oven up to 320°F (160 °C). Melt the butter in a pot, add milk and 1 vanilla packet (do not boil) and cool. Beat 4 eggs and 1 1/5 cups (270 g) of sugar, and combine the two mixtures.
Sift the flour with the baking powder and cocoa, add them to the resulting cream and pour everything into a baking dish (preferably rectangular), covered with buttered baking paper (it can be oiled and sprinkled with flour instead).
Beat the cream cheese, 1/5 cup (70 g) sugar and liquid cream, add the egg yolk and 1 vanilla packet. Beat again until you get a smooth cream. Pour the cheese mixture over the brown one and make patterns with a fork.
Bake for 50 minutes, then reduce to 284°F (140 °C) and bake for another 10 minutes. Cut the completely cooled brownie into squares.