Preheat oven to 400 degrees. Bake pie crust 8-10 minutes (you will finish baking later). Cool. NOTE: I use the rolled refrigerated pie crust. Before I put the dough in the pie pan, I will sprinkle a little flour in bottom of pan, put dough in pan and arrange, then sprinkle flour on the top of the crust and bake. This will help keep crust from being soggy. I do this when "blind baking" a pie shell for any kind of pie.
Line a baking sheet with paper towels, slice tomatoes and place in a single layer on the paper towels. Sprinkle liberally with salt. Drain 2 hours. This is an important step because the salt draws the liquid out of the tomatoes.
Heat oven to 350 to bake pie.
In bowl, chop basil and garlic, slice onions. Add mayo, sour cream and 1/2 of the cheese, saving the rest for the top of the pie. When tomatoes have drained well, place a layer of tomatoes in partially cooked pie shell, spread basil mixture over, layer the rest of the tomatoes and sprinkle with rest of cheese. Bake 45-60 minutes, depending on oven, until browned well. Remove from oven, let set about 20 minutes. Slice.