Crust:
Beat butter, sugar, and lemon zest in medium bowl until light and fluffy.
Combine flour, cornstarch and salt in a small bowl. Add butter mixture. Mix well. Press evenly in bottom and 1 inch up side of ungreased 10 inch springform pan with flat-bottomed glass. Bake in 350 degree F (175 degree C) oven for about 25 minutes until slightly puffed and golden. Let stand on wire rack to cool.

Filling:
Beat cream cheese and sugar in a large bowl until smooth. Add egg yolks, sour cream and vanilla. Beat on low until just combined.
Beat egg whites with clean beaters in medium bowl on high until stiff (not dry) peaks form. Fold into cream cheese mixture. Makes about 6 cups (1.5L) filling. Pour 3 cups (750 mL) filling into crust.
Put jam and flour into small bowl. Stir until blended. Fold 1/2 cup (125mL) filling into jam mixture.
Spoon 1/2 cup (125mL) jam mixture in small dabs over filling in pan. Cover with remaining filling and jam mixture in small dabs.

Cut through mixtures with blunt knife in swirling motion to create marble effect. Bake in 325 degrees F (160 degrees C) oven for about 1 1/4 hours until filling is almost set. Filling may still wobble in middle, but will set upon cooling. Immediately run knife around inside edge of pan to allow cheesecake to settle evenly. Cool completely. Cover. Chill for at least 6 hours or overnight.

Enjoy!