Combine crushed cookies and the 1/2 cup melted butter or margarine. Press firmly in bottom and 2 inches up sides of 9-inch springform pan. Chill. In mixer bowl, beat cream cheese and sugar till fluffy. Add eggs, one at a time, beating well after each addition. Blend in chocolate, the first cup sour cream, the 1/2 cup liqueur, the 4 tablespoons butter, and the vanilla. Pour into prepared crust. Bake in 350 degrees oven 65 minutes or just till set. Stir together remaining sour cream and liqueur; spread over cheesecake. Return to oven for 3 minutes. Cool, then cover and chill. Garnish with toasted sliced almonds.