Start by washing your preserving jars, screw bands and lids with hot soapy water; rinse well with warm water.
Open the cans and pour the sweetened condensed milk into the jars. The two cans should fill six small jars.
Place the lids on the jars and screw on the ring tops tightly. Place the jars in the slow cooker and fill with hot water so one-inch of water covers the tops of the jars. Cook on low for 10 hours.
After 10 hours, remove the jars with tongs. Be careful—it’ll be hot!
Place the jars on a dish towel until they cool down to room temperature. Gently remove the ring, and wipe off any water or rust that may have accumulated.
Store your cooked and cooled dulce de leche in the fridge for up to four weeks. To reheat, place jar in a saucepan filled with water half-way up the jar and bring to simmer.
Notes
Add a tag and some ribbon or twine, and your homemade gift is complete. Sweet!