Pumpkin Chiffon Mousse with Gingersnap Crust

Name: Pumpkin Chiffon Mousse with Gingersnap Crust
Ingredients: 20 (2-inch) gingersnap cookies, finely ground; 1/2 stick (1/4 cup) unsalted butter, melted and cooled; 3 1/2 teaspoons unflavored gelatin (from two 1 1/2-oz envelopes); 1/4 cup bourbon or brandy; 6 large eggs, separated; 3/4 cup packed light brown sugar; 2 1/4 cups solid-pack canned pumpkin; 1 1/2 teaspoons ground cinnamon; 3/4 teaspoon ground ginger; 3/4 teaspoon ground nutmeg; 1/2 teaspoon salt; 1/2 cup granulated sugar; 1 1/2 cups chilled heavy cream; Garnish: chopped crystallized ginger and whipped cream; a 9 1/2-inch (24-cm) springform pan