Invert bottom of a 9-inch springform pan, then lock on side and butter pan.
Stir together crumbs, pecans, sugars, and butter in a bowl until combined well. Press crumb mixture evenly onto bottom and ½ inch up side of pan, then chill crust for 1 hour.
Preheat oven to 350°F.
Whisk together pumpkin, eggs, brown sugar, vanilla, and liqueur (if using) in a bowl until combined.
Stir together granulated sugar, cornstarch, cinnamon, nutmeg, ginger, and salt in a large bowl. Add cream cheese and beat with an electric mixer at high speed until creamy and smooth, about 3 minutes.
Reduce speed to medium, then add pumpkin mixture and beat until smooth.
Pour filling into crust, smoothing top, then put springform pan in a shallow baking pan. Bake until center is just set, 50 to 60 minutes.
Transfer to rack and cool for 5 minutes. Leave oven on.
Whisk together sour cream, sugar, and liqueur (if using) in a bowl, then spread on top of cheesecake and bake for 5 additional minutes.
Cool cheesecake completely in pan on rack, about 3 hours. Chill, covered, until cold, at least 4 hours. Remove side of pan and bring back to room temperature before serving.
