- Open the can of sweetened condensed milk and divide evenly between the 2 canning jars.
- Wipe off any accidental spills of the tops and sides of the canning jars.
- Place a lid and ring on each of the canning jars and screw tightly to seal. Place the canning jars in a slow cooker and cover with water so is is 1 inch above the jars. Depending on your slow cooker and shape of your jars, you can lay the jars on their side or standing up straight. I was able to do mine standing up. Either way should work.
- Place the lid on the slow cooker and set to low for 8-9 hours, until the dulce de leche is deep golden brown. I did the full 9 hours.
- Carefully remove the jars from the hot water and let them cool. I found tongs work well to do this or use your canning supplies.
- Then, if desired, open the jars and stir in 1/2 – 1 teaspoon vanilla extract into each jar.I skipped this step.
- Replace the lids and rings and store in the refrigerator.
- Can be stored up to 1 month.