1. While bringing a large pot of salted water to a boil, melt butter in a large skillet over medium-high heat. Add leeks and a pinch of salt; cook until leeks begin to soften and are bright in color, about 4 minutes. Reduce heat to medium, and continue to cook, stirring occasionally, until very tender, about 5 more minutes. Turn off heat. Finely grate zest of lemons directly into skillet, and season generously with pepper.

2. When water boils, add sugar snap peas to boiling water, and cook until bright green, about 2 minutes. Transfer peas to a plate using a strainer.

3. Add pasta to boiling water, and cook until just tender, about 4 minutes (do not drain water). Transfer pasta to skillet using the strainer. Add sugar snap peas. Gradually stir in 1 cup pasta water, about 1/2 cup at a time, alternating with ricotta and half the Pecorino and tossing until pasta is coated and sauce is creamy.

4. Divide among 4 bowls, and top with remaining grated cheese.