For crust, in a food processor combine gingersnaps and the 2 tablespoons granulated sugar. Cover and process to form fine crumbs. With processor running, slowly add melted butter, processing until combined. Press mixture evenly onto the bottom of a 9-inch springform pan. Chill until firm.
Meanwhile, preheat oven to 350 degrees F. Place cream cheese in food processor. Cover and process until smooth. Add eggs, pumpkin, brown sugar, the 1/2 cup liqueur, the cinnamon, vanilla, ginger, nutmeg, and cloves. Cover and process until smooth, stopping once to scrape side of bowl. Pour filling over crust, spreading evenly.
Place springform pan in a shallow baking pan. Bake for 40 to 45 minutes or until edge is firm and center appears nearly set when gently shaken.
Meanwhile, for topping, in a medium bowl combine sour cream, the 1/4 cup granulated sugar, and the 1/4 cup liqueur. Transfer to a measuring cup with a lip. Without removing cheesecake from oven, pour topping over cheesecake, spreading evenly. Bake for 8 to 10 minutes more or until edge of topping just starts to bubble. Cool completely in pan on a wire rack. Cover loosely and chill for at least 12 hours.
To serve, loosen edge of cheesecake from side of pan; remove side of pan. Cut cheesecake while it is still chilled and firm. Let stand at room temperature for 20 minutes before serving. Sprinkle with hazelnuts.