How to Make It
Preheat the oven to 325°. Line a baking sheet with parchment paper. In a medium bowl, using an electric mixer, beat the butter with the sugar and vanilla until smooth. Add the all-purpose flour, rice flour and salt and beat just until combined. Quickly beat in the dried fruit. Pat the dough in an even layer 1/4 inch thick on the parchment paper. Bake for about 30 minutes, or until the shortbread is barely golden. Transfer the baking sheet to a rack and let cool. Increase the oven temperature to 375°.
Break the shortbread into small pieces and transfer to a food processor. Pulse until fine crumbs form.
Generously butter a 9-inch nonstick springform pan. Press the crumbs evenly over the bottom and 1/3 inch up the side of the pan.
In a large bowl, using an electric mixer, beat the Robiola cheese with the cream cheese until smooth. Beat in the sugar and vanilla seeds, then add the eggs, 1 at a time, beating well between additions. Beat in the sour cream, apricot nectar and sherry until blended. Beat in the cornstarch.
Pour the filling into the crust. Bake for about 15 minutes, then lower the oven temperature to 325° and bake for 15 minutes longer, until the center of the cake is still slightly jiggly. Transfer to a rack to cool, then refrigerate for at least 3 hours or overnight. Serve cold.