Cook pasta in a large pot of salted water according to package directions for al dente. Drain pasta and set aside.
In a large pot, melt butter over medium heat.
Whisk in the garlic and flour. Whisk until bubbling, about 1 minute.
Whisk in the beer, milk, pumpkin puree, dry mustard and salt. Bring the mixture to a boil.
Lower the heat and stir in 3 cups of cheddar cheese and the cream cheese. Stir until smooth. Add the pasta.
Transfer the mixture to a baking dish. Sprinkle the remaining 2 cups of cheddar cheese evenly over top. Bake 10-15 minutes, until bubbling. Garnish with fresh sage leaves and cracked black pepper, if desired.