I've never seen tomato leather, but I reckon it is just like any other fruit leather. Make a puree, spread it on a tray with a lining that won't let the juices leak or the puree fall through, and dehydrate it just like any other.
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The ultimate result of shielding men from the effects of folly is to fill the world with fools.
-- Herbert Spencer, English Philosopher (1820-1903)