Lemon Ripple Cheesecake Bars

Lemon Ripple Cheesecake Bars

Crust:
1 c. flour
1/4 c. sugar
1 tsp. finely grated lemon zest
1/8 tsp. salt
1 stick butter, cut into 1/2" pieces and chilled

Filling:
1 T. plus 2 tsp. cornstarch
1/2 c. cold water
2 egg yolks
1 3/4 c. sugar
1/4 c. fresh lemon juice
1 tsp. grated lemon zest
20 oz. cream cheese
2 T. flour
3 eggs
1/4 c. sour cream
1 tsp. vanilla extract

Preheat oven to 325 degrees.  Butter a 9" square nonstick baking pan.  Set the cream cheese and eggs out to bring them to room temperature.
In a food processor, pulse the flour with the sugar, lemon zest and salt.  Add the cold butter and pulse until a soft, crumbly dough forms.  Press the dough evenly over the bottom and 1/2" up the sides of the pan.  Bake for 20 minutes until golden brown.
In a small bowl, dissolve the cornstarch in the water.  In a medium saucepan, whisk the egg yolks with 3/4 c. of sugar and the lemon juice.  Whisk in the cornstarch mixture and cook over moderate heat, whisking gently, until the sugar is dissolved, about 4 minutes.  Boil for 1 minute, whisking constantly until the mixture is thick and glossy.  Put the mixture in a bowl and add the lemon zest.
In a large bowl, using an electric mixer, beat the cream cheese with the remaining cup of sugar until smooth.  Beat in the 2 T. flour until blended.  Add the eggs, one at a time, beating well.  Add the sour cream and vanilla and beat until smooth.  Pour the cream cheese batter over the crust and smooth the surface,  Dollop the lemon mixture on the cheesecake batter and carefully swirl into the batter.  Take care to not cut into the crust.  Bake the cheesecake for about 40 minutes or until just golden around the edge and just set.  Run the tip of a knife around the edge.  Let cool on a wire rack for 1 hour then refrigerate until thoroughly chilled.  Cut into 16 bars and serve.