Preheat the oven to 350° F (177° C) or prepare your steamer by filling the base with water and bringing it to a simmer.
Caramelize sugar in a saucepan over medium heat. Swirl to caramelize evenly. When the color turns dark amber, remove it from the heat immediately.
Divide the caramel between the molds. Tilt to coat the bottom evenly. It will solidify as it cools.
In a large mixing bowl, combine egg yolks and whole eggs. Whisk them together.
Add the evaporated milk, sweetened condensed milk, and vanilla extract. Whisk until incorporated.
Strain the custard into the molds.
Set a water bath by placing the custard-filled molds inside a large baking tray. Carefully add hot water until halfway up the side of the molds.
Bake the custard for about 45 minutes, until just set. When you gently shake the pan, it should slightly jiggle in the center. A toothpick or a knife inserted in the center should come out clean.
You can also steam them over simmering water (not boiling) on medium-low heat for about 30 minutes. Cover the molds with aluminum foil, as trapped steam can easily get into the leche flan.
Let them cool in the pan before refrigerating. It will take about 30 minutes until no longer warm to the touch.
Cover with plastic wrap and refrigerate a few hours before serving.
Run a knife along the edges of each mold to loosen the Leche Flan. Place a serving plate on top, then quickly flip it over to release it onto the plate.