Pre-heat your toaster oven or air fryer on "bake" setting to 350°F (175°C)
In a small pan, heat light brown sugar and water. Bring to a gentle simmer and swirl the pan occasionally. Once the sugar has caramelized and reached your desired color, immediately turn off heat.
Pour caramel into ramekin. Allow to cool and set.
In a bowl, break egg yolks and stir in one direction using a spatula.
Gradually add condensed milk, evaporated milk, key lime juice, and vanilla. Continue stirring in one direction until all the ingredients are well-blended. Do not over stir.
Place a fine mesh strainer over a glass measuring cup and pour the egg mixture.
Pour egg mixture over the prepared ramekin.
Place a pan on the oven tray. Gently transfer ramekin in the pan. Carefully pour hot water into the pan (bain marie, also known as water bath), not the ramekin. Cover with foil.
Slowly insert the tray into the middle of the oven.
Bake for 35 minutes or until the middle part comes out clean when a toothpick or knife is inserted.
Allow the Leche Flan and ramekin to completely cool. Refrigerate to chill.
Notes
Allow the caramel to set. The length will depend on the room temperature. If the weather is cold, it will set faster.Leche Flan tastes better once it’s chilled after several hours, but preferably after a day.Completely cool the ramekin before placing inside the refrigerator.If you have a sweet tooth and prefer a sweeter version of Leche Flan, add an additional 1 or 2 tablespoons of condensed milk.