2 c. blueberries for garnish
1 small bunch fresh mint
To prepare crust: Arrange a rack at center position and preheat the oven to 325 degrees. Generously butter the bottom and sides of a 9-inch springform pan with the softened butter. Wrap the bottom and sides of the pan tightly with a double thickness of aluminum foil. Have ready a large baking pan that will accommodate the springform pan.
Place crushed biscotti in the prepared springform pan. Add 2 tablespoons melted butter, mix well, and press onto the bottom of the pan to form an even layer. If the cookie mixture seems too dry, add up to 1 tablespoon additional melted butter. Bake the crust until golden, about 10 minutes. Set aside to cool while you prepare the filling.
To prepare filling: With an electric mixer on medium speed (using a flat paddle if you have one), beat cream cheese in a large mixing bowl until smooth and creamy, 2 to 3 minutes. Reduce speed to low and beat in the heavy cream until blended, about 1 minute more. Gradually add the sugar and lemon zest and beat until thoroughly combined, 2 to 3 minutes. If necessary, stop the mixer and scrape down the sides of the bowl with a rubber spatula.