Heat oven to 450°F. Grease bottoms and sides of six ramekins with 2 tablespoons butter; dust with cocoa powder.
Melt chocolate and ½ cup butter in a 2-quart saucepan over low heat, stirring frequently. Cool slightly.
Beat eggs and egg yolks in a large bowl with a whisk, until well-blended. Beat in Grand Marnier and powdered sugar. Fold in melted chocolate mixture and flour.
Divide batter evenly amongst ramekins, then place on cookie sheet.
Bake 12 to 14 minutes or until sides of cakes are set and centers are still soft. Let stand 3 minutes.
Serve with ice cream (optional).