Make the caramel: Heat 1/4 cup sugar (50 g) over medium heat. Gently swirl the pan instead of stirring. When the sugar turns a deep amber color, add the lemon juice, stir briefly, and pour into the flan molds. If the mixture is too thick, add 2 tablespoons water. Let cool at room temperature or refrigerate.

Separate 5 egg yolks. Whisk the yolks gently in a clockwise motion. Avoid beating too hard to prevent bubbles, which can cause holes in the flan.

Heat the fresh milk with the remaining 1/4 cup sugar (50 g). Let cool to about 120–140°F (50–60°C). Slowly pour the milk mixture into the egg yolks while stirring gently. Strain the mixture once through a fine mesh sieve. Add vanilla at this step.

For an extra smooth flan, strain the mixture 2–3 more times before pouring into the molds. Steam the flan for 30–40 minutes. Check doneness by inserting a toothpick—if it comes out clean, the flan is ready. Run a knife around the edge of the mold and invert onto a plate to release. Flan tastes best when served cold.