Bring a large pot of water to a boil and salt generously. Add pasta and peas. While pasta is cooking, mix together mashed garlic, ricotta, and tarragon in a large bowl. Season to taste with salt and pepper.

When the pasta is cooked al dente, remove (1/4 cup per 3/4 lb dry penne) of the pasta water and mix (2 to 4 tablespoons per 3/4 lb dry penne) of it with the ricotta. It should have the consistency of cream. Add a little more water if it doesn’t. Drain pasta and peas and toss with ricotta mixture and Parmesan. Serve at once.