How to Make It
Preheat oven to 350ºF. Spread walnuts on a baking sheet and bake for 5 to 10 minutes, until they’re lightly toasted and fragrant, shaking pan once or twice while baking. Transfer to a bowl.
Meanwhile, bring a pot of salted water to a boil. Cook pasta until al dente, about 10 minutes or as package label directs. Reserve 2 cups of cooking water before draining pasta.
Melt 1 Tbsp. butter in a large, deep skillet over medium-high heat. Add onion and cook, stirring often, until tender and translucent, about 4 minutes. Stir in garlic and sage and cook, stirring, for 1 minute. Stir in tomato paste and paprika; stir until combined.
Add pumpkin and cook, stirring, until well incorporated and warmed through. Add reserved pasta cooking water a few tablespoons at a time until desired consistency is reached. Whisk in yogurt and remaining 1 Tbsp. butter; cook until warmed through and butter has melted. Taste sauce and season with salt and pepper.
Toss pasta with sauce. Divide among 4 plates and top with Parmesan and reserved walnuts.