Dulce de leche: roughly translated, 'candy of milk,' and boy, is that spot-on! A decadent, creamy, complex treat that's as versatile as it is mouth-watering, traditional dulce de leche is notoriously temperamental when it comes to cooking. This method yields incredible results, while eliminating most of the babysitting and safety hazards associated with other methods.

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Step 1: Here's What You'll Need:

[quantities of each will vary based on the size of your slow cooker]

4 oz mason jars with lids and rings
14 oz cans sweetened condensed milk
1 clean kitchen hand towel
1 slow cooker

optional: flavorings such as salt, bourbon, bacon, fresh spices, vanilla bean, etc.

If you decide to use additional "chunks" stick to dryer, more shelf-stable ingredients. Also spring for the stuff that's a little pricier; especially bacon and bourbon. I'm using Bulleit bourbon here. It has very nice vanilla notes that pair exceptionally with desserts. Bacon should be cooked extra-crispy to prevent sogginess. Soggy bacon is sad bacon. Nobody likes how sadness tastes, and if they do, I don't want to meet them!

Step 2: Make the Bed

Fold your kitchen towel in such a way that it covers the entire floor of the slow cooker without going up the sides too much.

/!\IMPORTANT: DO NOT SKIP THIS STEP. YOUR JARS COULD EXPLODE WITHOUT A TOWEL BELOW THEM./!\

This will provide a stable, slip-free platform for the jars as well as a buffer against the direct heat from the ceramic.

Arrange your mason jars so that they each have some space around them. They should not touch each other or the wall of the slow cooker. I was able to fit 6 in my cooker.

Once they're arranged, you can begin filling with the sweetened condensed milk.

When using inclusions, I only fill the jar halfway at first, add my extras, then top off the jar with more milk, and stir it all together. This method prevents over-filling the jars and helps the inclusions incorporate more readily.

I aimed for just below the threads as my fill line. Don't go very much higher as these will expand during cooking, and you don't want to lose any of that milky goodness in the water bath [spoiler alert].

I ended up using a bit less than two of my 3 cans to fill the 6 jars. Open your cans one at a time to preserve the seal on unused cans.

Step 3: Full Metal Jar Lids

Now that your jars are full, you'll want to wipe the rims with a damp cloth or paper towel. There's definitely going to be some residue no matter how careful you are; condensed milk is messy stuff! Once your jar lips are blindingly shiny, you can add the lids, making sure to inspect the seals for any cracks, chips, or other defects that would prevent it from being airtight. Check the seals on new jars as well; you never know when a manufacturing defect will happen.

Next, screw the rings on, but don't tighten them all the way. I generally go until there's resistance then back off just a hair.

I labeled my lids for flavor variations with sharpies beforehand so they had plenty of time to dry.

Once the rings are on, check again to make sure there's space between all the jars and the wall.

Step 4: Fill 'er Up!

Cover the jars by at least 0.5 in of water at all times. I filled mine up the whole way which provided nearly 1 inch of coverage. Use the hottest water possible from your tap to give the cooker a head start.

Turn on your slow cooker, set it to high, and if it has a timer, set it for 2.5 hours.

This brings the water fully to temperature as quickly as possible and allows air to be forced out of the jars [that's why we left the rings slightly loose]. When the jars cool, a vacuum will form inside, sealing the lids on top. I believe it also results in greater complexity in the final product than cooking entirely on low; the blast of high heat for a short period followed by an extended period on low [more spoilers] gives the milk a head start on the maillard reaction.

After the 2.5 hours on high, check the water level. This should give you a good idea of how many alarms you'll need to set to top off the water. [Hey, I said we'd eliminate some of the babysitting, not all]

/!\IT IS VERY IMPORTANT TO KEEP THE JARS COMPLETELY SUBMERGED FOR THE ENTIRE COOKING PERIOD. THEY COULD EXPLODE IF COOKED DRY/!\

Don't worry as your jars start to bubble. This is the air being forced out by the expanding milk. Instead, Laugh maniacally as lighting flashes and thunder claps behind you, even though you're indoors; science is happening!

Step 5: Low & Slow

Now that we've topped off the water [remember to use hot water every time] we can set our cooker to low and cook for 9.5 more hours, for a grand total of 12 hours cook time.

Remember: how often you'll need to add water depends on your particular slow cooker. Be diligent. While there are failure points built into the jars, and we've taken care to keep them surrounded by water, accidents can happen. Do everything possible to minimize your risk of hot milky water and glass exploding all over your bedroom. [Hey, I'm not here to judge where you crock your pots]

And now: SCIENCE!

Step 6: SCIENCE!

Maillard Magic: This wonderfully addictive, creamy concoction is made possible entirely by a process called the Maillard [pronounced "my-yard"] Reaction.

Named, like many things culinary, after the dead French guy who discovered it, the Maillard reaction is what gives most cooked foods their brown color and complex flavors. A reaction, triggered by heat, between certain sugars and amino acids in food produces a plethora of new chemical compounds, many of which are still not fully understood.

The compounds produced are different for every food, as are the ideal temperatures and cooking speeds to produce the reaction.

In the case of dulce de leche, milk doesn't do well at high temperatures, so we need to keep it low, and it can separate if brought to temp too quickly, so slow was essential as well. In my opinion, the slow cooker is the ideal tool for the job.

Step 7: Dulce De Leche

Allow the jars to cool to room temperature in the water bath. The lids will pop downward as they cool; don't panic! They're not opening!

Finally! Though I think you'll find it was well worth the wait.

Please note: though we sealed the jars with a similar method to canning, this is no longer a canned product. The temperatures required to preserve a low-acid dairy product such as this are not possible in anything but a pressure canner. As such, its shelf life is about 1-2 weeks in the fridge, though I doubt it would stick around that long.

Dulce de leche is truly a magical substance. It can be used for virtually anything; between layers of cake, as a dip for fruit, stir into coffee, cocoa, tea, or just have a shot of it straight as an afternoon pick-me-up. ;) My favorite way to have it is drizzled over some vanilla bean ice cream with a bit of freshly grated nutmeg on top.

The bacon flavor goes amazingly well with waffles, the bourbon would be great layered between some dark chocolate cake, and the salted is actually surprisingly tasty with celery and carrot!

Please, experiment with flavors and let me know your favorites!

If you liked the Instructable, I'd really appreciate if you take a second to vote for it in any of the contests it's eligible for!

Thanks for reading; now go cook something!