In a medium bowl, whip the cream until it just holds soft peaks; whip in a chilled bowl for faster results.
Place the whipped cream and 4 glasses in the refrigerator to chill.
Stir together 2 teaspoons cinnamon and 1 teaspoon sugar in a small bowl and set aside.
Scoop the ice cream into a blender and pour 1/3 cup milk over the top.
Add pumpkin, maple syrup, ginger, remaining 1 teaspoon cinnamon and ice in the blender and pulse to combine; use a spoon to stir the ingredients between pulses, if needed.
Add a few tablespoons more milk, if desired, depending on how thick you like your milkshakes; blend until smooth; it may seem thick at first, but once poured, it will melt fairly quickly.
Pulse in the bourbon, if using, and divide among the four chilled glasses.
Spoon the whipped cream over the top and sprinkle with cinnamon sugar.
Drizzle with caramel sauce, if desired.
Notes
Whip the cream and store in an airtight container, in the refrigerator, up to overnight.