A now-buried thread about Chapeau! that morphed into a discussion of "fallen" or "molten" chocolate cakes (link below) included garcon's request for my recipe. Here it is (adapted by me from one that appeared in Bon Appetit magazine).
This recipe is for two servings, and can be multiplied. The cakes can be flavored with an extract (e.g., mint, almond) or liqueur of your choice if you wish. The most difficult part is the timing of the baking; check at 20 minutes, but don't go more than a few minutes longer. If they come out too soon, they'll collapse when unmolded, but if they go too long, they won't be "molten" inside. And by the way, the molten part is gooey and fudgy, and does NOT taste like raw cake batter. They are best served with ice cream and/or a fruit sauce.
MOLTEN CHOCOLATE CAKES
2 ounces bittersweet chocolate, chopped
1/4 cup (half stick) unsalted butter
1/4 cup sugar
2 tablespoons unsweeted cocoa
2 large egg yolk
1 large egg
1 teaspoon vanilla extract
2 teaspoons all purpose flour
Generously butter two 6-ounce ramekins or custard cups and dust with flour or cocoa powder. Melt chocolate and butter over low heat or in microwave. Whisk until smooth. Whisk in sugar and cocoa, then egg yolk, then whole egg, then vanilla, then flour. Divide batter among ramekins. At this point, you may cover and refrigerate ramekins for up to a day. When ready to bake, preheat oven to 350F. Bake cakes uncovered until edges are set but center still looks shiny and tester comes out with some wet batter attached, 20-22 minutes. Let rest for 5 minutes, then run a thin knife around sides of ramekins and invert cakes onto plates. Serve immediately.