Add milk and sugar to a heavy-bottomed medium-large pot (a Dutch oven works great). Heat the milk over low-medium stirring occasionally until the sugar dissolves.
720 grams milk,, 200 grams sugar
Once the sugar dissolved, turn the heat up to medium-high and bring milk to a simmer but don't boil it. Let the milk simmer for 45-60 minutes (until it starts to thicken and turns a yellowish creamy color).
Don't stir the milk during sthe immering process. To check for consistency, turn off the heat and wait till the milk stops simmering, then check consistency with a spoon.If the milk is too runny, simmer for another 5-10 minutes and check again. If it starts to thicken, take it off the heat and run through a strainer to get rid of larger bits.
Allow the milk to cool to room temperature before transferring it to the refrigerator, where it will continue to thicken as it chills. Serve and enjoy!
Notes
Tips:
If you accidentally boil sweetened condensed milk, simply remove the milk skin after it's done simmering and strain it to get rid of lumps.
Make sure all sugar dissolves before simmering the milk or it will crystalize.
Raise the heat carefully until you reach the simmering stage and check on the milk occasionally to avoid boiling or burning it.
Don't be afraid to raise the heat, if your milk is only barely bubbling, it will take longer to make sweetened condensed milk.
Don't stir condensed milk while simmering to prevent crystallization.
Homemade sweetened condensed milk will last in the fridge for up to 1 month in an air-tight container.
You can freeze sweetened condensed milk for up to 3 months. If it separates after thawing, just give it a good whisk to restore its smooth consistency!