Rather than discard leftover tomato skins, you can turn them into a delicious and easy tangy-sweet powder with this recipe.
Line a microwave-safe plate with a double layer of paper towels. Spread as many of your leftover tomato skins on top as will fit in a single, non-overlapping layer.
Microwave on high for 4 minutes, then continue in 20-second intervals until the skins are papery, dry, and crumble if pinched. Repeat with remaining skins.
Add leftover tomato skins, salt, and sugar to a spice grinder or mortar and pestle. Grind until powdered. Store in an air-tight container.