4 tablespoons (1/2 stick) butter
½ cup bittersweet chocolate chips
1 egg yolk
3 tablespoons granulated sugar
⅛ teaspoon salt
1 tablespoon natural cocoa powder
Preheat the oven to 450°.Liberally grease two 7-ounce ramekins - it's crucial that the cakes don't stick! I used a paper towel to spread softened butter all around the inside of each ramekin. You can also sprinkle a little flour after you grease the ramekins, although the second time I made these I did not use flour and they slid right out.Combine the butter and chocolate in a glass bowl set over a pot of simmering water. Stir until melted.In a separate bowl, beat the egg with the egg yolk, sugar and salt on high until thickened and pale. This will take a good 3-4 minutes, so be patient. Scrape down the side of the bowl as needed.Whisk the cocoa powder into the melted chocolate, and then quickly whisk the mixture into the eggs. Don't overmix - stop once everything is incorporated.Spoon the batter into the ramekins. Bake for 10-12 minutes, until the sides are firm and the centers are still soft, but not jiggly. A minute can make a big difference, so keep an eye on the cakes.Let the cakes cool for 1 minute in the ramekins, and then set a plate face-down on top of each ramekin. While wearing an oven mitt, carefully flip the ramekin and plate over. Let stand for 10 seconds and then carefully lift the ramekin.
Adapted from: http://veggieandthebeastfeast.com/2014/01/28/molten-nutella-lava-cakes-for-two/