Preheat the oven to 375°F. Generously butter a 9-inch springform pan.

In a large metal bowl set over simmering water, melt the butter and chocolate together until smooth. Remove from the heat and stir in a pinch of salt. Let cool.

Place egg whites into the bowl of a stand mixer (or other large mixing bowl) and the yolks into a small bowl. Stir the yolks to blend with a fork, them stir into the cooled chocolate.

Beat the whites with the whisk attachment (or hand-held mixer) until stiff. Add a third of the beaten whites to the chocolate and stir with a wooden spoon or rubber spatula to lighten the batter. Gently fold on remaining whites and pour into prepared pan.

Bake for 12-13 minutes.

Remove from oven - the center should be jiggly.

Let cool 10 minutes on a rack. The sides should have shrunk from the edges a bit. Run a thin-bladed knife or spatula around the edges to loosen. Let cool completely in pan.

Remove the outer ring from the springform pan and slide onto a serving plate.

Slice into small wedges. Serve with a small dollop of Raspberry Sauce or freshly whipped cream.