Preheat the oven to 450 degrees F. Grease and flour 4 (6-ounce) ramekins or baking dishes with the 1 1/2 teaspoons of butter and 1 teaspoon of flour in each, tapping out the excess flour. Set on a baking sheet.
In a double boiler, or a metal bowl set over a pan of simmering water, melt the remaining 1/4 pound of butter with the chocolate, cream, and powdered sugar, stirring until smooth. Remove from the heat.
In a bowl, whisk together the eggs, egg yolks, sugar, vanilla, and salt until thick ribbons form, about 3 minutes. Sift 2 tablespoons flour into the egg mixture and fold together. Fold the chocolate into the egg mixture. Divide among the prepared dishes and bake until the sides of the cake are set and the tops are puffed but still soft, about 12 minutes.
Remove from the oven and let cool in the ramekins for 2 minutes, then unmold onto dessert plates.
Meanwhile, in a bowl whip the cream until beginning to form soft peaks. Add the sugar and nut liqueur and beat until stiff peaks start to form. Spoon a dollop of the whipped cream on each unmolded cake, and garnish each plate with raspberries and a sprig of mint. Sprinkle cocoa over the cakes, and serve.
Yield: 4 servings