Molten Bittersweet-Chocolate Cake

Butter and flour six 6-ounce (2-inch-deep) ramekins.

Melt butter and chocolate in a double boiler or a heatproof bowl set over a pan of simmering water. Meanwhile, whisk together eggs and sugar until pale and thick, about 4 minutes. Sift flour and salt into another bowl.

Fold egg mixture into chocolate mixture. Immediately fold in flour mixture. Divide batter evenly among ramekins, filling each three-quarters full. Transfer to a rimmed baking sheet. Refrigerate for at least 1 hour.

Preheat oven to 400 degrees. Bake until just set, 14 to 16 minutes. Let cool for 3 minutes. Turn out cakes onto plates.