Instructions:
First Layer:
First, dissolve the cornstarch in a small amount of cold milk.

Then, in a saucepan, combine the remaining milk, sugar, vanilla extract, and the cornstarch mixture.

Cook over medium heat, stirring constantly, until you achieve a thick and smooth cream.

After that, transfer the cream to a container and let it cool.

Second Layer:
Start by melting the sugar in a saucepan over low heat until it forms a golden caramel.

Next, add the margarine and mix well until fully incorporated.

Afterward, pour all the cold milk at once, stirring continuously to prevent lumps.

Then, dissolve the cornstarch in water and add it to the caramel.

Cook over medium heat, stirring, until the mixture thickens.

Assembly:
To begin, spread the first cream layer evenly in a glass dish.

After that, pour the caramel layer over the first one, leveling it with a spatula.

Finally, refrigerate for at least 40 minutes before serving.

Tips:

Decorate with chocolate shavings, fresh fruits, or whipped cream for an extra touch.
Serve chilled to enhance the flavors.