Boil the pasta by bringing a large pot of salted water to a boil, adding the pasta and cooking until al dente, about 8-10 minutes. Drain and reserve a cup of pasta water.

Prepare the sage brown butter by melting the salted butter in a skillet over medium heat. Add sage leaves and sauté until the butter turns golden brown and the sage is crispy, about 4 minutes. Remove sage and set aside.

Sauté garlic and chili flakes in the brown butter on medium-low heat for about 1 minute until aromatic, without browning the garlic.

Incorporate pumpkin purée and apple cider into the skillet, mixing well. Simmer for about 2-3 minutes until it slightly thickens.

Add whole milk gradually, bringing the sauce to a gentle simmer. Cook for 5 minutes until the sauce thickens.

Blend in the grated Parmesan and gouda cheese, stirring until melted and creamy, seasoning with salt and pepper.

Combine the drained pasta with the sauce, tossing to coat evenly. Cook for an additional 3-5 minutes while adding reserved pasta water if the sauce thickens too much.

Serve by plating the pasta and garnishing with crispy sage. Enjoy the warm flavors immediately!