8 tablespoons butter, plus extra for coating
3 tablespoons flour, plus extra for dusting
1/2 cup sugar, plus extra for dusting
10 ounces semi-sweet chocolate, chopped
4 large eggs
1 large egg yolk
1 teaspoon vanilla extract
1/4 teaspoon salt
1/2 cup mini marshmallows
2 tablespoons unsweetened cocoa powder
1. Preheat oven to 375. Generously butter, flour and sugar eight 6 ounce ovenproof mugs. Wipe the rims clean.
2. Place butter and chocolate in a pan over simmering water and melt, stirring once or twice. Remove from heat and cool for 5 minutes.
3. Use a mixer to beat eggs, yolk, vanilla and salt until mixture doubles and becomes foamy, about 5 minutes.
4. Stir the 3 tablespoons of flour into the chocolate and then add to the egg mixture, beating on low until fully incorporated.
5. Ladle batter into each cup until it is 1/2 inch from the rim. Bake until cakes puff but centers are still runny, 13-17 minutes. Remove from oven, sprinkle each cake with marshmallows and return to the oven until puffy, about 2-4 minutes. Let cool for 5 minutes, sprinkle with cocoa powder and serve.