Preheat oven to 350 degrees F.
First, begin by making the caramel. In a saucepan over very low heat, cook sugar until it turns a deep amber color and all the crystals have melted. Tilt the pan so the sugar melts evenly. DO NOT USE ANY UTENSIL.
Once sugar has caramelized, pour it quickly into an 8 inch round pan. It's okay if the sugar crystallizes because once the flan is baked, the caramel will melt.
To make the flan custard, crack 4 eggs in a large mixing bowl and whisk together (I use my large 1 quart measuring mug).
Slowly add in condensed milk and mix it into the eggs really well. (Condensed milk is quite thick so I like to add it before evaporated milk).
Finally pour in the evaporate milk along with vanilla and whisk really well.
Pour this mixture over the caramel.
Next, place the pan in a roasting tray filled half way up with water. This is called water bath. This will ensure that the flan evenly bakes in the oven.
Bake for 55-60 minutes or just until the edges are set and the center still wobbles a little bit when you shake the pan.
Let the flan cool on the counter before placing it in the fridge for a 3-4 hours to set.
When ready to unmold, run a knife under hot water, wipe it clean, and then run it along the edge of the pan.
Shimmy the pan a little and invert the flan onto a large serving dish. Make sure the dish has raised edges to catch all that melted caramel.
Slice and enjoy!