milk; cover and blend at low speed 2 min. Add 3 T sugar, egg yolks and vanilla; blend at medium speed until well mixed. Add cottage cheese; blend at high speed until smooth. Remove 3/4 c mixture to use for marbling; chill until mixture begins to thicken. Combine 1 T sugar and cocoa; add to blender container and blend until mixed. Pour chocolate mixture into large bowl. Chill, stirring occasionally, until mixture mounds when dropped from spoon. In small bowl with electric mixer at high speed, beat egg whites until foamy. Gradually add remaining 2 T sugar; beat until stiff peaks form. Fold beaten whites into chocolate mixture; pour chocolate mixture into prepared crust. Spoon large dollops of vanilla mixture over chocolate; with knife or spatula, gently swirl to create marbled effect. Cover; refrigerate until firm, about 4 to 5 hours. Chocolate Crumb Crust In small bowl, combine crumbs and cocoa; add butter and stir until evenly blended. Press mixture evenly on bottom of 9 in. springform pan.