Make the caramel:

First, add 1/4 cup sugar (50 g) to a pot, then pour in 1/2 cup water (100 ml). The water will help dissolve the sugar evenly and prevent it from sticking to the sides and burning or crystallizing.

When the sugar turns a nice amber color, add the lemon juice and turn off the heat. Quickly swirl about 1 tablespoon of caramel into each prepared mold to coat the bottom with a thin layer.

Slowly pour the warm milk mixture into the egg yolks, stirring constantly to prevent curdling. Add 1 teaspoon vanilla extract and mix well. Strain the mixture through a fine mesh sieve 1–2 times to remove bubbles, which will help the flan turn out smooth.

Pour the custard into the caramel-lined molds. Do not fill the molds completely—fill them about 3/4 full, as the flan will expand as it cooks.

Bake the flan:

Oven method: Place the molds in a baking tray and fill the tray halfway with hot water. Bake at 300–320°F (150–160°C) for about 40 minutes. Baking time and temperature may vary depending on your oven and mold size.

Air fryer method: Preheat the air fryer for 10 minutes at 230°F (110°C). Place the molds in the air fryer and bake for about 35 minutes until set.

Steaming method: Cover the molds tightly with foil or heat-resistant plastic wrap to prevent water from dripping onto the flan. Prepare a steamer, place the molds inside, and steam at 175–195°F (80–90°C), below boiling, for 15–20 minutes. To check if the flan is done, insert a toothpick—if it comes out clean and the hole is dry, it's ready.

Rice cooker method: Add enough water to the rice cooker, place the molds inside, cover the top with a clean cloth, and close the lid. Press “Cook” and steam for about 20 minutes. When the cooker switches to “Warm,” the flan is done.