1. Wash kumquats in warm, soapy water and rinse well. Pierce each one in a few places with a fork to prevent bursting while cooking.

2. Bring water to a boil in a medium saucepan over medium-high heat. Add kumquats and simmer until tender, 5 to 10 minutes. Remove with a slotted spoon and drain.

3. Add sugar to water and bring to a boil. Let boil 5 minutes and add drained kumquats. Simmer for about 1 hour, or until fruit is completely transparent. Remove from heat, cover pot, and allow fruit to sit overnight.

4. Heat oven to 250 degrees. Drain kumquats well in a colander, discarding syrup. Space evenly on a parchment-lined baking sheet and leave in oven from 2 to 4 hours, or until they feel somewhat dry and tacky. Roll kumquats in sugar, if desired. Store in a single layer in an airtight container for up to 3 weeks.