Preheat the the oven to 200F (or 170F if your oven can go lower) and make sure to set to convection oven settings. Then, line a tray with parchment paper and set aside.
Use a mandoline or a very sharp knife to slice the citrus into slices no more than ¼" in width. If the slices are thicker, they will take longer to cook.
Place the citrus slices onto the parchment lined tray and bake anywhere from 3-6 hours depending on the size of the citrus. Lemons and Limes take the least amount of time followed by oranges and lastly grapefruit which will take the longest.
After about 2 hours of baking, flip the citrus so the side facing the parchment paper is now exposed. Also, rotate the tray so that the citrus that was closest to the glass is now in the back of the oven. Continue this process every 2 hours as needed.
Once the citrus has no more moisture and is brittle to the touch, remove from the oven and let cool completely.
Use as a cocktail garnish, topping on a baked good, or blend into a citrus sugar. Enjoy!