• Hands-On Time: 20 minutes
  Total Time: 55 minutes
  Makes 6 to 8 servings
• 8 tablespoons (1 stick) unsalted butter, plus extra for the cups
  10 ounces semisweet chocolate, roughly chopped
  
4 large eggs
1 large egg yolk
1 teaspoon vanilla extract
1/4 teaspoon kosher salt
1/2 cup granulated sugar, plus extra for the cups
3 tablespoons all-purpose flour, plus extra for the cups 1/2 cup miniature marshmallows
2 tablespoons unsweetened cocoa powder
• 
  

Heat oven to 375° F.

Generously butter, flour, and sugar eight 6-ounce ovenproof coffee cups, mugs, or ramekins. Wipe the rims clean.

Place the butter and chocolate in a large heatproof bowl. Set it over a pan of simmering water, and heat, stirring once or twice, until melted and smooth. Remove from heat. Let cool for 5 minutes.

With an electric mixer on medium-high, beat the eggs, egg yolk, vanilla, salt, and 1/2 cup of the sugar until the volume doubles and the mixture becomes foamy, about 5 minutes. Stir the flour into the chocolate mixture, mixing until incorporated. Reduce speed to low and slowly add the chocolate mixture to the egg mixture, mixing until incorporated. FIll each cup about 1/2 inch from the rim. Bake until the cakes puff and begin to crack on the surface but are still a bit runny in the center, 13 to 17 minutes, depending on the size of the cups. Remove from oven. Sprinkle with the marshmallows and return to oven until the marshmallow begins to crisp, 2 to 4 minutes. Remove from oven. Let cool for about 5 minutes. Sift the cocoa over the top.

Tip: If you prefer a larger cake, bake the batter in a 9- or 10-inch springform pan and use regular-size marshmallows to cover.  You will need to increase the baking time to 17 to 20 minutes for a gooey center, 22 to 25 minutes for a mildly fudge-like interior.