Hot Chocolate Cake

Directions

1. Preheat oven to 375° F. Generously butter, flour, and sugar eight 6-ounce coffee cups or mugs made of ovenproof stoneware. Wipe the rims clean.
2. Place the 8 tablespoons of butter and the chocolate in a medium heatproof bowl over a pan of simmering water and melt, stirring once or twice until smooth. Remove from heat and let cool 5 minutes.
3. Using a handheld mixer, beat the eggs, yolk, vanilla, salt, and 1/2 cup sugar at the highest speed until the volume doubles and the mixture becomes foamy, about 5 minutes. Stir the 3 tablespoons of flour into the chocolate, then gradually add it to the egg mixture, beating on low until it's fully incorporated.
4. Ladle the batter into each cup until it's about 1/2 inch from the rim. Bake until the cakes puff and begin to crack but the centers are still a bit runny, 13 to 17 minutes. Remove from oven. Sprinkle with marshmallows, then return to oven for 2 to 4 minutes, until the marshmallow tops begin to crisp. Remove from oven; let cool about 5 minutes. Sift the cocoa on top.