This is a very rich and very delicious dessert drink. The float is only for presentation and should be mixed before you drink it. I would strongly recommend that you make your own chocolate syrup using high quality, high cacao content chocolate.   Fill the shaker with ice. Add 1 oz. gin to the shaker. Add 1 oz. black cherry flavored brandy. Add 2 1/3 oz. fresh chocolate sauce. Shake well. Pour the drink up to 1/3rd of the glass. (chilled champagne glass) Fill a clean shaker with ice. Add 1 oz. vanilla yogurt to the shaker. Add some gin. Shake well. Pour slowly over a spoon in the champagne glass to make the topping. Garnish with some fresh grated dark chocolate.