Lots of regional variations can be found but they all use the basics--- tomatoes, cheese, and mayonnaise --- and produce a summery taste treat that can get by for a few hours unrefrigerated, and is just as good at room temperature as it is warm from the oven. It's a welcome side dish , brunch addition, or appetizer served in smaller slices. Leftovers at our house reappear at breakfast. I've seen several types of cheese used; basil added, and other variations but my preferred recipe is simple and always includes bacon, because what isn't improved by bacon?
Bake a 9" pie crust as directed, and cool it. Cut about 3 nice ripe medium tomatoes into 1/4" slices, drain on a paper towel for 30 minutes and put them in the crust. Sprinkle with 10 slices of crisp bacon, crumbled. In a bowl, combine 1 c. shredded cheddar cheese with 3/4 c. real mayonnaise. Low fat or low calorie mayo can't be used. Spoon over the center of the pie, leaving about an inch exposed around the edges. Bake in a preheated 350 oven for about 30-40 minutes. The pie crust and topping should be golden brown. Check at about 20 minutes and cover edges with foil if they are browning too much. Let cool a bit if planning to indulge right away. If the topping seems a bit runny, it may be due to using very juicy tomatoes or various brands of mayonnaise -so reduce the amount a bit. Or switch to good ole Hellmann's. And even on the occasions when it doesn't cut perfectly, it tastes awesome.