In a saucepan over low heat, melt butter and chocolate together. Set aside. In a mixing bowl, combine sugar and cornstarch. In a separate bowl, whisk eggs and yolks together. Add the melted butter - chocolate mixture to the sugar mixture; whisk thoroughly. Stir in eggs; whisk until smooth. Grease 4 ramekins with cooking spray. Fill ramekins two - thirds full with mixture; chill overnight.
Preheat oven to 400 degrees. Bake on the top oven rack for 20 minutes. Remove from the oven.
FOR THE WHITE CHOCOLATE SAUCE: In a saucepan over low heat, combine chopped white chocolate and cream. Stir mixture constantly until melted. Remove from heat. Stir in the liqueur and orange rind; set aside.
Dust souffles with powdered sugar and poke one small hole in the center of each souffle. Pour white chocolate sauce into hole. Serve immediately.