For the caramel, beat the eggs with the sugar. Add the vanilla and beat once more. Then add the milk. Leave it aside and get to work on the layer.
For the layer, mix the flour with the cocoa and baking powder. Beat the egg together with the sugar. After they have been beaten well, add the flour with the cocoa and baking powder, oil and milk. Beat the mixture until homogeneous. Caramelize 5 tbsp of sugar in a cake form 8 3/4″ (22 cm) in diameter.
While it's still warm, pour in the caramel mixture which you've beaten beforehand. Then, pour the mixture for the layer in the middle of it. Be sure to pour it in right in the middle, it sinks first and then rises.
Put the cake form in a larger oven dish with water. Bake in a preheated 356°F (180 °C) oven for about 50 min. After it's ready, leave the cake to cool and put it in the fridge for 12 hours. Then, invert it onto a platter and serve.