For the crust:
1 1/4 cups ground almond biscotti
1/4 cup granulated sugar
6 tablespoons unsalted butter melted, plus more for coating the baking pan
For the filling:
1 package cream cheese, cut into pieces
225g whole-milk ricotta, drained in a fine sieve for 30 minutes to get rid of excess moisture
3/4 cup granulated sugar
2/3 cup heavy cream
4 large eggs, separated
Finely grated zest from 1 medium orange
1 teaspoon pure vanilla extract
1/4 teaspoon kosher salt
For the topping:
1/2 cup blood orange marmalade
2 tablespoons water
1. Preheat the oven to 180°C and arrange a rack in the middle. Coat the bottom and sides of a pan with butter.
2. In a bowl, stir together biscotti crumbs, sugar and melted butter until the crumbs are evenly moistened. Pour into the prepared pan and press evenly onto the bottom. Bake until set, about 8 minutes. Let the crust cool on a wire rack. Reduce the oven temperature to 150°C.
3. To make the filling, in the bowl of a food processor, process the cream cheese until smooth. Add the ricotta, sugar, cream, egg yolks, orange zest, vanilla and salt and process until smooth, about 2 minutes; scrape down the sides of the bowl and process again. Pour the mixture into a large bowl.
4. In another bowl, beat the egg whites to medium-stiff peaks.
5. Using a rubber spatula, fold about one-third of the whites into the cream cheese mixture. Then gently fold in the remaining whites. Pour into the crust and spread evenly.
6. Bake for 30 minutes, then increase the oven temperature to 160°C. Continue baking until the surface is golden and the centre still jiggles slightly when gently shaken, about 30 minutes longer. Turn off the oven and let the cake cool in the oven for 1 hour. Remove the cheesecake from the oven and let it cool on a rack for about 30 minutes.
7. To make the topping, in a saucepan over low heat, warm the marmalade and water, stirring constantly, until melted and combined. Let cool about 5 minutes. Spoon the glaze over the top of the cheesecake, spreading evenly. Let the cheesecake cool completely.
8. Cover and refrigerate the cheesecake until well chilled, at least 2 hours or preferably overnight.
9. Remove the pan sides and run a long, thin knife between the pan bottom and the crust, slide the cake onto a serving plate, and serve.