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