Wash fruits thoroughly.
On a chopping board, using a sharp knife, cut fruits into 1/8-1/4 inch slices. (You can use a mandolin). Remove any seeds.
Fill a bowl with very cold water and set aside.
Place a cooling rack over a baking sheet, set aside.
Add some water to a medium-size pot, bring to a boil, reduce to a rolling simmer.
Add Lemon and orange slices, simmer for 3 minutes then take them out immediately and place in the bowl of cold water.
Repeat two or three times, changing the water each time. (This is called blanching.
In a saucepan, put 2 cups water and 2 cups sugar. Place over medium-high heat. Bring to a boil, boil until sugar has melted.
Add fruit slices, spreading them out as much as you can. Reduce to a simmer.
Simmer for 60 to 90 minutes depending on the thickness of the slices.
When they are tender, translucent and the liquid has reduced considerably, turn off the heat.
Leave to stand in the syrup for at least two hours. Remove slices and place on a cooling rack.
Leave to air dry overnight or in a warm oven. Store the remaining syrup in an airtight jar.