Boil the milk and let it cool. Put 150 g of sugar in a saucepan and melt it slowly over low heat until it is a dark brown, but not burnt.
As soon as it is ready, pour it hot in the oven tray (20 x 20 cm) and distribute it very quickly with a spoon on the whole surface and a little on the walls. If you do not move quickly, the caramel hardens and you do not manage to spread it, in this case it must be reheated a little in the oven.
If you melt the sugar right in the tray, be very careful if it is glass. However, melt over low heat and carefully, or use a saucepan, or metal tray. The advantage here is that the caramel is distributed more evenly on the surface of the tray.
In another deep bowl, mix well 7 eggs with 250 g of sugar and vanilla essence. Add the cooled milk and mix well. Pour the composition into the bowl with the caramelized walls.
In a larger oven tray (large enough to fit the cream bowl) pour as much water as you can and place the bowl with the cream composition. It is very good to follow this step, otherwise the cream may bake too much on the sides and bottom and has a porous texture.
Put the tray with water and the pot in it in a preheated oven at 160 ⁰C for 40-45 minutes.
The cream is ready when it browns a little on top and is firm to the touch. Allow to cool completely to room temperature. Then cover with foil and put in the fridge for a few more hours.