Mix flour, egg yolk, and milk into a smooth, thin crepe batter. Heat a crepe pan on medium low and melt 1/4 teaspoon of the butter. Add 1 tablespoon of batter, and flip the crepe after it sets. Fill it with dulce de leche, and set aside. After making all the crepes, heat the rum with sugar, when it ignites, pour over the crepes and serve at once.
Dulce de Leche:
Scald milk in heavy bottom sauce pan. Add all other ingredients, cook on medium low until it turns into caramel, about 1 hour.