Remove the label. This is optional, but I think it's easier to peel dry paper off of a can than to fish wet particles of disintegrating paper out of hot water when you're done.

Clean the glue off the can. This is also optional, but every brand of sweetened condensed milk that I tried had such a strong glue attaching the label to the can that afterward, the interiors of my pots (stock pot, Instant pot, and Crock pot) were covered in a grimy film from the glue. I'd rather clean the glue off the can than clean it off my pot. I used Goo Gone and it took about 2 seconds.

Place the can on it's side (not upright) in your pot (Crock pot, Instant pot, or large stock pot). This is so that the can stays put on the bottom of the pot. It will bounce around if you stand it upright. You can make as many cans at a time as you like, usually up to 3 depending on the size of your pot. The cans need to be able to to fit sideways on the bottom of the pot, do not stack them.

Alternatively, you can scrape your sweetened condensed milk into a very clean mason jar and seal tightly with a clean ring and a clean lid. If you choose this method, place the jar in the pot upright, not on it's side. If you are doing more than one can, make sure they are not touching each other. Leave a little space at the top of the jar so the milk has room to expand.  2 (14 ounce) cans of sweetened condensed milk will fit into 3 (8 ounce) mason jars. Mason jars are perfect if you are planning to gift these to neighbors or friends.

Fill your large stock pot with water that reaches 2 inches above the cans (which are on their sides.)

Cover with a lid and set over high heat.

When the water is at a rolling boil, lower the heat to a simmer. For my stove on the "power burner" this was on low. There should still be active bubbles, just not so much that your water looks ragey and angry. It should be gently bubbly.

Simmer as is for 3 hours. Keep the lid on. Check the pot every 30-60 minutes to make sure that the water level is above the cans. The cans need to be completely submerged at all times. Add more hot water as necessary.

After 3 hours, either wait for the water to cool a bit, or carefully remove the can with tongs and oven mitts. DO NOT open the can right away! The can is pressurized and you will spurt yourself with molten hot dulce de leche, and it will hurt. You can place the can in a bowl of cold water to speed up the cooling if you like. When you can handle the can easily with your bare hands, it is ready to be opened. It doesn't take more than a half hour if placed in cold water.

Open your can and voila! Delicious dulce de leche!

Fill your Instant pot (or any brand electric pressure cooker) with water that reaches 1 inch above the cans (which are on their sides.)

Place the lid on the Instant pot and turn the lever on top to "SEAL."

Pressure cook on high (which is the default) for 40 minutes.

At this point you can either release the lid naturally or follow manual instructions to do a quick release. Be careful! You don't want to get a steam burn.

DO NOT open the can right away! The can is pressurized and you will spurt yourself with molten hot dulce de leche, and it will hurt. You can place the can in a bowl of cold water to speed up the cooling if you like. When you can handle the can easily with your bare hands, it is ready to be opened. It doesn't take more than a half hour if placed in cold water.

Open your can and voila! Delicious dulce de leche!

Fill your slow cooker with water that reaches 1 inch above the cans (which are on their sides.)

Set the heat to LOW and cook for 8-10 hours. The longer you cook it, the darker your dulce de leche will be.

After 8-10 hours, either wait for the water to cool a bit, or carefully remove the can with tongs and oven mitts. DO NOT open the can right away! The can is pressurized and you will spurt yourself with molten hot dulce de leche, and it will hurt. You can place the can in a bowl of cold water to speed up the cooling if you like. When you can handle the can easily with your bare hands, it is ready to be opened. It doesn't take more than a half hour if placed in cold water.

Open your can and voila! Delicious dulce de leche!

If you do not open the cans, they are shelf-stable for 3 months . There is no need to refrigerate if you have not opened the cans. They are still sealed. If you cooked in mason jars, they are not shelf stable and you need to refrigerate.

Once the can is opened, transfer leftovers to a mason jar with a lid or a tupperware with a lid. Refrigerate for up to 3 weeks.

The consistency of dulce de leche after cooling is pudding-like. It is not thin or pourable. It is more like soft peanut butter. If you are storing in the fridge, you can warm it in the microwave for a minute or two to soften it. If you are pouring over ice cream, I like to stir in a bit of cream to the warm dulce de leche to make it even smoother. Because calorie restraint is not my forte :)