For the bottom crust, preheat oven to 350 degrees F. Line the bottom of a 9-inch spring form pan with foil and grease, or parchment paper.
In a food processor combine flour, sugar and pecans. Pulse briefly. Add unsalted butter; pulse until mixture resembles fine crumbs. Press crust mixture evenly into bottom of prepared pan. Bake for 20-25 minutes until lightly golden. Cool and grease sides of pan.
For the filling, increase oven temperature to 500 degrees F.
In a mixer, using paddle attachment add cream cheese, salt, and sugar. Beat until combined and fluffy. Add Mascarpone, lemon juice and vanilla. Beat on low speed until just blended.
Add eggs and egg yolks two at a time. Beat on low speed until eggs are incorporated.
Place pan on cookie sheet. Reserve 1 1/2 cups of the filling, pour remainder of the filling onto the prepared crust. Stir 1/2 cup of chocolate sauce into the reserved filling. Place dollops of the chocolate filling on top of cake. Drag a knife through chocolate forming a swirl pattern.
Bake 10 minutes. Reduce heat to 200 degrees F and bake 1 1/2 hours keeping oven door closed. When done, top will be golden and center will be almost set. Cool, then refrigerate covered overnight. Garnish with chocolate shavings and chocolate drizzle.