Cook the pasta in a large pot of boiling salted water, stirring occasionally, until a tad under al dente, 7 minutes (or 2 minutes less than package instructions). Add the asparagus and continue to cook, stirring, for 1 minute. Add the peas and cook until hot, about 1 minute more. Reserve 1/2 cup of the pasta cooking liquid, and then drain the pasta, asparagus, and peas together.
Transfer the pasta and vegetables to a large bowl—or back to the now empty pot if preferred. Add the butter, lemon juice and zest, sour cream, 1 teaspoon salt and the pepper. Toss, adding the reserved pasta cooking liquid as needed, until a smooth sauce coats the pasta (you may not need all of it).
Divide the pasta among plates or bowls. If the basil leaves are small, you can use them whole. If not, tear or thinly slice them as desired. Top the individual plates with the salmon and basil, and enjoy.