Preheat the oven to 350F, and butter and flour an 8 inch cake pan. Set aside.

In a heatproof bowl set over a pot of simmering water, gently melt the chocolate and butter until smooth and creamy.

In a medium bowl, beat together the egg yolks and sugar until a light and fluffy cream forms. Still whisking, slowly add in the melted chocolate mixture until smooth, then add in the flour.

In the bowl of a stand mixer, beat the egg whites until stiff peaks form.

Add about half of the beaten egg whites to the chocolate mixture to lighten it, then gently fold in the remaining whites. Pour the batter into your prepared pan, then bake for about 10 minutes.

Remove the pan from oven, and quickly press the chocolates evenly around the edges of the cake.

Return the cake to the oven for 20-25 more minutes, until the middle no longer jiggles and the top has crackled slightly.

Let cool before removing from pan, and serve with powdered sugar and whipped cream. Enjoy!