This single serving flan is a smooth caramel custard made from scratch for one. It's easy to make and comes out silky and rich, with a caramel top that runs down over the custard when you turn it out.
Adjust an oven rack to the middle position and heat the oven to 350°F (177°C).
In a 1-quart saucepan, stir 2 tablespoons sugar with 1 tablespoon water over low heat until the sugar dissolves, about 2 minutes.
Raise the heat to medium-high and boil the syrup without stirring until it turns deep amber, about 7 to 9 minutes, swirling the pan now and then and watching closely near the end.
Immediately pour the caramel into a 10-ounce ramekin and tilt it to coat the bottom.
In a small saucepan over medium-low heat, warm the milk with 2 tablespoons sugar just until the sugar dissolves and the milk is warm to the touch, about 2 minutes. Don't let it boil.
In a bowl, whisk the egg, then slowly pour in the warm milk in a thin stream while whisking constantly so the egg doesn't cook, and whisk in the vanilla and salt.
Pour the custard through a fine-mesh strainer into a bowl or measuring cup to remove cooked egg and air bubbles.
Pour the strained custard into the caramel-lined ramekin.
Set the ramekin in a larger baking dish and add hot water to the outer dish until it reaches halfway up the sides of the ramekin, taking care not to splash any into the custard.
Bake for 45 minutes, until the edges are set but the center still jiggles slightly when nudged.
Let the flan cool in the water bath for 1 hour.
Cover and chill in the refrigerator for at least 12 hours or up to 3 days.
To serve, run a thin knife around the edge, set a plate on top, flip, and lift off the ramekin.
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Notes
Have everything ready before you start: The caramel and the warm milk both come together fast, so measure your ingredients and set your ramekin next to the stove before you turn on the heat.Stop stirring once the caramel boils: Set the spoon down when the syrup comes to a boil and just swirl the pan now and then. Stirring boiling sugar can turn it grainy instead of smooth.Use a 10-ounce ramekin: In a smaller dish, the caramel pools too thick to melt all the way through as the flan bakes, and you end up with a hard layer stuck at the bottom. The 10-ounce size spreads it thin enough to turn back into sauce.Don't skip the water bath: The ring of hot water around the ramekin keeps the custard cooking slow and even. That gentle heat is what holds the texture smooth and keeps it from curdling or cracking.Take it out while the center still jiggles: Your flan's done when the edges look set but the middle wobbles as you nudge the dish. It firms up as it chills.