Asparagus and sausage pasta

This simple pasta is for in-between seasons - it marries the richness of a wintry pasta with the verdant vibrance of spring. The combination of sausage and butter glosses everything in a silky sauce, while the asparagus, frozen peas, lemon and an entire cup of basil keep it springy. (There are more vegetables in there than sausage or pasta.) Feel free to use coarsely-chopped springtime alliums like leeks, spring onions or ramps instead of the shallot.