Make the Caramel:
Place a saucepan on the stove and add a little water (previously boiled and cooled). Add 1/4 cup sugar (50 g) and cook over low heat. Stir constantly until the sugar dissolves and turns a deep amber color. Add the lemon juice, stir well, and remove from heat.

Prepare the Custard:
Separate the egg whites and yolks into two bowls. Place the yolks in a clean mixing bowl. Gently whisk the yolks in one direction until fully combined.

Add the remaining 1/4 cup sugar (50 g) and the milk to a saucepan. Heat over medium until the milk is warm (do not let it boil). Gradually pour the warm milk into the beaten yolks from step 2, stirring gently to combine until smooth and uniform.

For a silky flan, strain the mixture through a fine mesh sieve several times to remove any lumps. Stir in the vanilla. Pour the smooth custard mixture into molds that have been coated with the caramel.

Steam the Flan:
Place the filled molds in a steamer and steam for 30 to 40 minutes. Cover the top of the steamer with a towel or cheesecloth before placing the lid on, to prevent water droplets from falling onto the flan and creating an uneven surface.