Make the crust: Position a rack in the lower third of the oven and preheat to 350 degrees F.
Spread the almonds for both the crust and topping (1/4 cup plus 1/3 cup) on a rimmed baking sheet and bake until golden, about 5 minutes.
Let cool. Crumble the biscotti into a food processor; add 1/4 cup toasted almonds and the granulated sugar and pulse until finely ground.
Add the butter and pulse to combine. Press the mixture into the bottom of an 8-inch springform pan.
Bake until set, about 12 minutes, then transfer to a rack and let cool completely. Reduce the oven temperature to 300 degrees F.
Meanwhile, make the filling: Beat the egg yolks and 1/2 cup granulated sugar in a large bowl with a mixer on high speed until pale, about 2 minutes.
Add the ricotta and beat until smooth, about 2 more minutes. Beat in the amaretto, vanilla and almond extracts, and orange zest.
Put the egg whites and the remaining 2 tablespoons granulated sugar in a separate bowl and beat with a mixer on medium-high speed until soft peaks form (do not overbeat). Using a rubber spatula, fold about one-third of the beaten egg whites into the ricotta mixture, then gently fold in the rest until just combined. Scrape the batter into the prepared crust.
Bake until slightly puffed and lightly golden on top, about 1 hour, 20 minutes.
Transfer to a rack and let cool, 20 minutes. Run a knife around the edge of the cake to loosen, then remove the springform ring and let cool completely.
Combine the confectioners' sugar and cinnamon in a fine-mesh sieve and dust over the cheesecake. Scatter the remaining 1/3 cup toasted almonds on top and dust again.
Serve at room temperature. Photograph by Johnny Miller
