In a saucepan over low heat, melt the sugar until it caramelizes.
Pour the caramel into a baking dish, spreading it evenly on the bottom.
In a large mixing bowl, combine the sweetened condensed milk, evaporated milk, eggs, and vanilla extract.
Whisk until well combined.
Strain the mixture through a fine sieve into the baking dish with the caramel.
Cover the baking dish with aluminum foil.
Place it inside a larger baking pan and fill the larger pan with water halfway up the sides of the flan dish.
Bake for about 50-60 minutes or until the flan is set but still jiggly in the center.
Remove from the oven and let it cool.
Refrigerate for at least 4 hours or overnight.
To serve, run a knife around the edges of the flan and flip it onto a plate.
Notes
For a twist, you can add grated citrus zest or a splash of rum to the flan mixture. No alcoholic drinks allowed, please substitute with a non-alcoholic option.