Preheat oven to 350 degrees. Prepare Sour Cream Pastry.
Sour Cream Pastry: Stir together first 3 ingredients in a bowl. Cut shortening into flour mixture with a pastry blender until mixture resembles small peas. Add sour cream; stir with a fork until combined. Gently gather dough into a flat disk; wrap in plastic wrap, and chill 1 to 24 hours.
Tomato Pie: Meanwhile, place tomatoes in a single layer on paper towels; sprinkle with salt. Let stand 30 minutes. Pat dry with paper towels. Stir together next 3 ingredients and 3/4 cup of cheese.
Roll Sour Cream Pastry into a 13-inch circle on a lightly floured surface. Fit into a 9-inch pie plate; fold edges under, and crimp.
Bake at 350 degrees for 10 to 12 minutes or until lightly brown. Remove from oven, and sprinkle remaining 1/4 cup cheese over bottom of crust. Arrange tomato slices over cheese in crust; spread mayonnaise mixture over tomatoes.
Bake at 350 degrees for 34 to 37 minutes. Let cool 5 minutes before serving.