In a large saucepan, heat the margarine over low heat. Add the marshmallows and mix until they are well melted and the preparation is homogeneous. Remove the pan from the fire.
Pour vanilla extract and Rice Krispies cereals, mix to coat well.
Pour the mixture into a large buttered mold and flatten with a lightly buttered spatula. Let cool for at least 1 hour before cutting into squares.
Melt the chocolate in a bowl. Dip the face of each square of Rice Krispies in melted chocolate and place on a plate for the chocolate to freeze.
Enjoy the Rice Krispies chocolate squares at tea time.