Preheat oven to 425 degrees. Using a silicon pastry brush, prepare the inside of four 6-ounce ramekins with melted butter.

In a small bowl, whisk the cocoa powder with 1 tablespoon of the flour; dust the ramekins with the cocoa mixture, tapping out the excess. Transfer the ramekins to a sturdy baking sheet and set aside.

In a medium saucepan, melt 1 stick of butter with the chocolate over very low heat, stirring occasionally. Let cool slightly.

In the bowl of a stand mixer fitted with a paddle attachment, beat the granulated sugar with the eggs and salt at medium-high speed until thick and pale yellow, 3 minutes. Using a silicone spatula, fold in the melted chocolate until no streaks remain. Fold in the 1/4 cup of flour.

Spoon the batter into the prepared ramekins. Bake in the center of the oven for 10-12 minutes, until the tops are cracked but the centers are still slightly jiggly. Transfer the ramekins to a cooling rack for 5-8 minutes.

Run the tip of a small knife around each cake to loosen. Invert a small plate over each cake and, using potholders, invert again. Carefully lift off the ramekins. Dust the warm cakes with confectioners' sugar. Serve immediately with optional whipped cream or ice cream.