1 cup plus 2 tablespoons unsalted butter, softened
To make the crust:
Line a 13- x 9-inch pan with aluminum foil and grease the foil with butter. In a bowl, combine biscotti crumbs and butter. Press into bottom of prepared pan and freeze.
To make the filling:
In a mixer bowl fitted with paddle attachment, beat cream cheese, mascarpone cheese, sugar and flour until very smooth, for 3 minutes. Add whole eggs and egg yolks, one at a time, beating after each addition. Mix in wine and vanilla. Preheat the oven to 325 degrees F.
Pour over the frozen crust, smoothing out to sides of pan. Bake in a preheated oven until top is light brown and center has a slight jiggle to it, 45 to 55 minutes. Let cool in pan on a wire rack for 2 hours. cover with plastic wrap and refrigerate for at least 6 hours before cutting into bars. Serve with cherry-kirsch sauce or truffle fudge frosting with lots of chocolate shavings.
To make the frosting
In top of double boiler over simmering water, melt milk and bittersweet chocolate, stirring until smooth. Let cool until no longer warm to the touch.
In a mixer bowl fitted with whip attachment, beat butter and melted chocolate on medium speed until uniform in color, about 3 minutes. Place bowl in the refrigerator for 10 minutes to firm the frosting. Return to the mixer and beat until fluffy, about 2 minutes.
Decorate the cheesecake any way you want it with the frosting!