I had my first tomato sandwich shortly after I read Harriet the Spy for the first time, back when I was 8 or 9--I had never had one before, and I was intrigued to see why Harriet demanded that sandwich every day. Turns out that sliced tomatoes and mayonnaise is a fabulous combination--I am convinced that it's a big part of the reason that BLTs are so good.
Our vegetable garden is coming into its own now, and we have an abundance of homegrown tomatoes to work with. So far our favorite variety is the Cherokee Purple, a dark red heirloom with great flavor.
Tomato sandwiches work even with average tomatoes, but when you have great tomatoes to work with they become sublime. All you need is some bread--either sandwich bread or a crustier loaf. I like mine lightly toasted so that it doesn't get too soggy from the tomato juices. Spread the bread liberally with mayo (I go for Hellman's/Best Foods), top with sliced tomato, and season with salt and pepper. Lately I've been making mine open faced, so as to maximize the tomato.
Even mayo skeptics can be converted to the cult of the tomato sandwich--just ask my husband. We'll be having these for lunch every wekend until we run out of tomatoes. If you've never had one, get the best tomatoes you can find and give it a try.