Cook the penne in boiling water until al dente or past (depending on your preference) and drain.
While the pasta is cooking, grate the zest of the lemons. Squeeze and reserve the juice of one lemon (juice the other lemons, too, and freeze the juice for another recipe).
In a small saucepan, warm up the olive oil, add the zest, and cook over low flame for two minutes. Add the sour cream and bring to a boil; pour in the reserved lemon juice and bring to a boil again.
Add the Parmesan, and season with salt and pepper to taste. Mix well and cook for another minute.
Pour over the drained pasta and stir to coat the pasta with the sauce.
To make this for less, I buy the olive oil in bulk at Sam's Club. I buy the sour cream on sale for $1.25. I buy parmesan cheese at Winco. I buy pasta on sale a couple of times a year for .50 a pound. The lemons above are Meyer lemons from my garden, but I have found lemons in bulk at Walmart (in bags) for about .20 each.