Cook the pasta in boiling salted water according to package directions. Drain and set aside.

Melt the butter in a large skillet. Add the lemon juice, zest, salt and red pepper flakes and mix.

Take the skillet off the heat and slowly add the yogurt (or sour cream). The sauce will appear to break---don’t worry! Immediately add the linguine, Parmesan cheese and pepper. Toss well.