For fruit puree: combine fruit in a blender with 1/2 to 1 cup water and blend until you get a mixture the consistency of applesauce. For best results, use ripe, sweet fruits like you would pick if you were making jam.
To the fruit puree, add corn syrup, lemon juice and cornstarch. Blend until smooth. Pour the puree into a saucepan and bring to a boil. Reduce heat to medium and let simmer for 2 minutes. Let cool and taste. Add more corn syrup as needed to reach the desired sweetness.
Pour cooked puree onto dehydrator fruit leather drying sheets. Slap the sheets on the counter a couple times to level the liquid. Place sheets on racks in the dehydrator and dehydrate at 125 degrees for 10 to 12 hours or until the leathers easily peel off the drying sheets.
Peel the leathers off the drying sheets and place them on the mesh racks of the dehydrator and dehydrate another 2 to 3 hours. This will help remove any remaining tackiness.
Remove from the dehydrator and roll up in wax or parchment paper while still warm. Store in Ziploc bags in a cool, dry place for up to a year.