Serves 2; Prep time: 10 minutes; Total time: 35 minutes
If you want to double or triple this recipe, just add 3 minutes or so to baking time. To make ahead, cover ramekins with plastic wrap after step 2; refrigerate up to 1 day. Bake 14 to 16 minutes.
2 tablespoons unsalted butter, plus more for ramekins
1/3 cup confectioners' sugar, plus more for ramekins and serving
2 ounces semisweet chocolate, broken into pieces
1 large egg
1 large egg yolk
1 teaspoon espresso powder
3 teaspoons all-purpose flour
1. Preheat oven to 400°. Butter two 6-ounce ramekins, then dust with sugar. Place butter and chocolate in a microwave-safe bowl. Microwave on high in 20-second increments, stirring after each, until melted. Let cool slightly.
2. Meanwhile, in a small bowl, whisk together egg, egg yolk, sugar, espresso powder, and salt. Add chocolate mixture; whisk to combine. Add flour, and whisk just until combined (do not overmix). Pour batter into prepared ramekins. (Recipe can be made ahead up to this point.)
3. Bake until a toothpick inserted 1/2 inch from edge of ramekins comes out clean, and a toothpick inserted in center comes out wet, 10 to 12 minutes (do not overbake). Cool 10 minutes on a wire rack. Run a knife around inside of ramekins to loosen. Invert cakes onto serving plates. Dust with sugar; serve immediately.