Slice the tomatoes into thick slices, about 1/2 inch thick. Lay them on a baking sheet and give them a little showering of salt and pepper.
Spoon about 1/2 to 3/4 tsp of balsamic onto each tomato slice, making sure to bathe the entire top.
Roast the tomatoes for 2 hours, until they soften up and contract a bit.
Carefully scoop the tomatoes up with a spatula, and layer them with a slice of mozzarella, and basil leaves. Drizzle with olive oil and sprinkle with a little flaky sea salt, to taste. Enjoy with crusty baguette, or all by itself!