Cook pasta according to the package instructions, until al-dente.
Drain (keep ½ cup of the pasta water) and drizzle with some olive oil.
Place a deep bottom nonstick pan over medium/high heat.
When the pan is hot, add 2 tablespoon of the olive oil and the mushrooms.
Cook until mushrooms are lightly browned.
Reduce heat and simmer until mushrooms are tender about 8 minutes.
Remove mushrooms from the pan and set aside.
Set the heat to medium/high again and add the rest of the olive oil.
Add the leeks and cook until soft. Then add the garlic and sauté for 2 minutes.
Add the pumpkin puree, the milk, and the cheese or nutritional yeast and stir.
Let the sauce cook and when it starts to bubble add the pasta and the mushrooms.
If you like a thinner sauce add the ½ cup of water and toss through.
Serve while still warm. Top it with some chili flakes, freshly ground black pepper, and more (vegan) cheese.
Enjoy :)