Step 1

Preheat the oven to 350°F (180°C) and grease a 9-inch (23 cm) springform pan with butter.

Step 2

In a medium saucepan over very low heat, melt butter and dark chocolate, stirring constantly to prevent chocolate from burning. Turn the heat off and stir in sugar. Add the eggs, one at a time and whisking vigorously after each one, to prevent the eggs from cooking. Then gently fold in the flour and stir until smooth.

Step 3

Pour the batter into the springform pan and bake for 15-17 minutes. The sides of the fondant cake should be almost done while center is slightly jiggling. Remove from the oven and let cool completely before serving.