• Preheat oven to 350°F (177°C).

For the caramel layer:

• In a medium saucepan over medium heat, combine sugar and water.
• Let the sugar dissolve and caramelize without stirring (you can swirl the pan gently). Cook for about 6-8 minutes until caramelized and deep golden brown or amber in color.
• Immediately pour the sugar mixture into the bottom of your baking pan, quickly tilting to coat the bottom evenly before it sets. Be careful—it’s hot and it hardens quickly. Set aside.

For the flan:

• Bring a kettle of water to a boil (for the water bath).
• Beat the eggs with a whisk until smooth. Combine sweetened condensed milk, whole milk, beaten eggs, and vanilla with a whisk until well combined and smooth. Avoid over mixing to prevent incorporating too much air. Let any bubble settle before adding to the baking pan.
• Pour the custard gently over the caramel in your pan.
• Place the pan into a larger baking dish and pour hot water around it to come halfway up the sides (this is your water bath).
• Bake for 50 to 55minutes, or until the center jiggles slightly like gelatin but is mostly set. A toothpick inserted should come out mostly clean, just like cakes do.
• Remove from the water bath and let cool to room temperature.
• Cover and refrigerate for at least 4 hours or overnight.
• When ready to unmold, run a thin knife around the edges. Then, dip the bottom of the pan in warm water for about a minute, then invert it onto a plate. The caramel will flow beautifully over the flan.