Bring a large pot of water and the salt to a roiling boil. Add the pasta and cook for 10-12 minutes.

Before draining the pasta, reserve 1 cup of the pasta water. Drain the pasta in a colander and let it sit for 1 minutes. Dump the penne into a large bowl and stir in the pesto and 1/4 cup of pasta water. Add salt and pepper to taste and check the sauce. If it's too sticky, add a bit more water. Serve hot with parmesan cheese.