Heat a large saute pan over medium-high heat.
Add the oil and sweat the onion for 2 minutes, stirring often, then add the garlic and the squash and saute for 1 minute.
Add the white wine to the pan and allow to reduce by half, then add the chicken stock.
Bring to a simmer, then reduce heat to low and cover with a lid.
Simmer gently for 20 minutes or until the squash has become soft.
Remove the pan from the heat and puree the squash with the cooking liquid in a blender until smooth. If the puree is too thick, thin out with a little water.
Strain the puree through a fine-mesh strainer, season to taste with salt and pepper and reserve.
While the squash is cooking, bring a large pot of salted water to the boil.
Once the puree is made, add the pasta to the water and cook for 8 to 10 minutes or until al dente.
While the pasta is cooking, heat a large saute pan over medium heat.
Add the oil to the pan and sweat the onions and leek for 2 minutes, stirring often.
Add the garlic and fennel to the pan and continue cooking for an additional 3 minutes.
Add the snow peas and the wine and allow the wine to reduce by half, then add the sauce to the pan and mix well.
Strain the pasta into a colander set in the sink, then add the drained pasta to the pan of vegetables and sauce.
Add the butter and, using a pair of tongs, toss well to mix and season to taste with salt and pepper.
Using a two-pronged meat carving fork, swirl a quarter of the pasta onto the fork and mound the pasta onto the center of a warm pasta bowl in a spiral shape, then repeat with remaining pasta and bowls.
Spoon the remaining vegetables from the pan evenly over the pasta in the 4 serving bowls.