Pasta with walnuts, ricotta, and lemon

I went looking for campanelle pasta recently, because I wanted to try a new Martha recipe, but I drew a blank at my local market.  Instead of subbing in another twisty pasta shape, I decided to go with orechette, one of my new favorites...you'll be seeing more of it here!  Here's the original recipe for Campanelle with Walnuts, Ricotta, and Lemon.  I made a half-recipe, and it was more than enough for two of us.