Preheat the Oven to 350°F (175°C). Gather equipment: 7-inch round cake pan, larger roasting pan, and aluminum foil.

Make the Caramel by combining sugar and a splash of water over medium heat. Stir until sugar dissolves and begins to bubble. Cook until golden brown, about 8-10 minutes, then pour into the bottom of the prepared pan.

Prepare the Custard by whisking together eggs, sweetened condensed milk, whole milk, and vanilla extract until smooth. Avoid creating air bubbles.

Create the Bain Marie by pouring the custard mixture over the caramel in the prepared pan. Cover with aluminum foil and place it in the larger roasting pan filled with hot water halfway up the sides.

Bake for 1 hour and 15 minutes. Check for doneness; the center should jiggle slightly but not be liquid.

Cool the flan at room temperature for 30 minutes then refrigerate for at least 4 hours, or overnight.

Unmold the Flan by running a knife around the edges, placing a platter over the top, and quickly inverting it. Allow caramel to drizzle over the flan.