In a non-stick flan mold you add the sugar (evenly spread) and you leave it to cook on the stove until it reaches a dark color. Heat oven to 350 F. When you see this reaction, remove the mold from the stove and make sure that it is evenly spread so that you can leave it to cool off.
Mean while, mix in a blender the 3 eggs, the La Lechera Condensated Milk, the regular milk and the tea spoon of vanilla (extract). After it is well mixed, place it in the flan mold where the cold caramel had rested. To cook, fill baking pan with 1/2 inch of warm water, and cover with a tent of aluminum foil. Bake until custards are just set, 30 to 40 minutes. Remove pan from oven, and remove custards from pan.
Serve when cooled, or cover flans with plastic wrap and refrigerate until ready to unmold. To unmold, run a knife carefully around the edge of each custard. Invert onto a plate, and drizzle 1 teaspoon of coffee liqueur, if using, over each flan.