In a blender or mixing bowl, combine 4 large eggs, 1 (14-ounce) can of sweetened condensed milk, 1 (12-ounce) can of evaporated milk, and 1 tablespoon of vanilla extract. Blend or whisk until completely smooth.
Once the caramel has set, carefully pour the custard mixture over the hardened caramel in the cake pan.
Preheat your oven to 350°F (175°C). Place the cake pan inside a larger baking dish, and fill the larger dish with hot water until it reaches halfway up the sides of the cake pan.
Carefully place the baking dish in the preheated oven. Bake for about 50-60 minutes, or until the flan is set but still slightly jiggly in the center.
Once baked, remove the flan from the oven, and let it cool in the water bath for about 10 minutes. Then, remove the pan from the water bath and let it cool to room temperature. Cover with plastic wrap and refrigerate for at least 4 hours, or overnight for best results.
To serve, run a knife around the edges of the flan to loosen it. Place a serving plate on top of the pan and quickly invert it. Slice into wedges and enjoy!