Heat oven to 350°F. Line a 9-in. round baking pan with foil, letting foil extend above pan on opposite sides; coat with nonstick spray.
Process crackers in food processor until fine crumbs form. Add butter and egg white; pulse until crumbs are moistened. Using bottom of a small measuring cup, press evenly over bottom of pan. Bake 10 minutes or until firm and set. Cool.
Whisk cream cheese, sour cream, 1/2 cup sugar, and the eggs in a large bowl until smooth. Remove 1/4 cup. Pour remaining batter over crust.
Stir cocoa, 2 Tbsp water and 3 Tbsp sugar in a cup to mix. Stir into reserved 1/4 cup batter until blended. Spoon over filling, then drag a toothpick or skewer through filling in a spiral motion to create marbled effect.
Bake 30 minutes or until firm around edges but slightly jiggly in center. Cool in pan on rack in refrigerator at least 3 hours until firm.