Add this to baked goods like biscuits or use it to rim a cocktail glass.
Preheat oven to 150° or as low as it will go. Using a vegetable peeler, remove peel from fruit. Place peels in a large saucepan and pour in cold water to cover. Bring to a boil and cook 1 minute. Drain; rinse peels under cold water. Repeat twice more.
Spread peels out on a wire rack set inside a rimmed baking sheet and bake until dry and brittle, 18–24 hours.
Working in batches, grind peels in a spice mill to a fine powder.
DO AHEAD: Powder can be made 1 month ahead. Store airtight at room temperature.