To make the caramel sauce, heat a medium-sized sauté pan over medium heat. When pan is hot, add 1/2 cup sugar, water, and lemon juice; do not stir.
Cook approximately 6-7 minutes or until the mixture turns burnt orange in color. Do not overcook as the sauce will become bitter.
Evenly distribute the sauce between 4 individual flan molds.
Using a large mixing bowl, beat the eggs. Slowly add 1/2 cup sugar while continuing to beat.
Stir the vanilla in the milk. Add the milk to the egg mixture and mix well.
Using a sieve, strain the mixture into a pitcher to remove the excess egg particles.
Evenly distribute mixture into the flan molds. Transfer flan molds to a 2-inch deep casserole dish. Carefully, pour water into the casserole dish to cover the flan molds half-way up on the sides. Cover with foil. Bake for 45 minutes.
After 30 minutes of cooking time, check the flans, they should jiggle when done. Remove from the oven and remove flan molds from the casserole dish. Cool for approximately 45 minutes.
Using a paring knife, gently run a knife around the outside edges to detach the flan from the mold. Place a serving plate over the flan mold, flip to remove.