I used two cans of condensed milk and found 2 little jam jars; washed them clean and poured 1 can of sweetened condensed milk into each. I sealed the tops as tightly as I could by hand.
I then placed them in my Slow Cooker and completely covered them with hot water from the sink; hot water speeds up the process. I set it on high for 4 hours
and walked away and when it was done, I drained the water and set the cooked sweetened condensed milk cans on the counter to cool. From my reading you can also set it on low for 6-8 hours overnight.
The dulce de leche was perfect. The right color and texture. No mysterious chemicals and now I get to lick the spoon.
When choosing a brand of condensed milk, just make sure the ingredients are simple.
Notes
If not using right away, refrigerate any un-used portion of dulche de leche.