Pasta with Mascarpone Pumpkin Sauce and Toasted Walnuts

Farfelle pasta

butter

medium onion, finely diced

garlic cloves, minced

minced fresh sage

pumpkin puree, fresh or canned

Kosher salt and freshly ground pepper

mascarpone cheese (sub cream cheese if necessary)

freshly grated Parmesan cheese

For the Garnish::

walnuts, toasted and rough chopped

snipped chives

Parmesan cheese, grated