Oreo Double Chocolate Cheesecake

1/4 cup butter or margarine
25 Oreo Chocolate Sandwich Cookies, crushed
16 ounces cream cheese (at room temperature)
6 eggs, separated (at room temperature)
4 (1 ounce) squares semisweet chocolate, melted
2 teaspoons vanilla extract
1/2 cup granulated sugar
1 (1 ounce) square semisweet chocolate
Chocolate curls

In a medium saucepan, over low heat, melt butter or margarine. Remove from heat. Stir in Oreo crumbs. Press evenly onto bottom and sides of a 9-inch springform pan; refrigerate while preparing filling.

In a large bowl, with electric mixer at medium speed, beat cream cheese until light and fluffy; beat in egg yolks, melted chocolate and vanilla extract until smooth, about 3 minutes; set aside.

In another large bowl, with electric mixer at high speed, beat egg whites until soft peaks form. Gradually add sugar, beating until stiff peaks form. Using a rubber spatula, gently fold beaten egg white, one-third at a time, into cream cheese mixture. Pour into crust. Freeze for 4 hours.

In a small saucepan, over low heat, melt the 1 (1 ounce) square semisweet chocolate; remove from heat; let cool to room temperature.

On an 11 x 8 1/2-inch sheet of white paper, draw 1 (6-inch) circle; on outside of circle, draw 12 (1-inch) circles, spaced evenly around circle. Place on cookie sheet; cover with wax paper, securing wax paper edges under cookie sheet.

Use a No. 1 decorating tip, pipe melted chocolate onto wax paper over outline (or drizzle chocolate, a little at a time, from teaspoon); freeze until firm, about 30 minutes.

Remove sides of pan; carefully remove wax paper from chocolate loop decoration. Set on frozen cheesecake. Garnish with chocolate curls.