1/2 pound (2 sticks) unsalted butter, plus more for greasing
1/2 pound bittersweet chocolate, at least 60 percent
1/2 cup granulated sugar
3 large eggs
3 tablespoons cake flour
Preheat the oven to 350 degrees F. Butter 4 (6-ounce) ramekins and set aside.
Over a double boiler, melt the butter and chocolate, whisking until smooth. Make sure to whisk until the chocolate and butter have combined into a smooth chocolate mixture. Whisk in the sugar, making sure most of the sugar dissolves in the warm chocolate mixture.
In a medium bowl, whisk the eggs until smooth. Pour the chocolate mixture in to the eggs. Whisk until smooth, then add the flour and combine until smooth. Pour the batter into the prepared ramekins about 2/3 full. Bake the cakes until slightly puffy and set around the edges, 20 to 25 minutes. Don’t worry if your cake tester comes out wet, the center should still be loose. Serve warm.