How to Make It
Preheat the oven to 350°. Butter four 1/3 cup ramekins.
Heat the olive oil in a small skillet. Add the onion and cook over moderate heat, stirring, until softened and lightly browned, about 8 minutes. Transfer to a food processor and puree. Let cool, then add the egg, cream and half-and-half and process until combined. Strain into a bowl.
Melt the butter in a small skillet. Add the apple and cook over high heat, stirring, until browned and just tender, about 3 minutes. Let cool. Stir the apple into the custard and season with salt and pepper. Pour into the ramekins.
Set the ramekins in a small baking dish and add enough hot water to the dish to reach two-thirds of the way up the sides of the ramekins. Bake for about 25 minutes, or until the flans are firm. Remove from the water bath and let stand for 10 minutes. Run a small knife around the flans and unmold them onto plates.