Begin by washing and drying the containers or jars you plan to fill. Set aside.
Cut the mangos into rough cubes and place in a large, flat bottomed container.
Mash the mangos with a potato masher until the mixture looks soupy. This will leave some small bits of the mango intact and give the jam a bit of texture.
Use a measuring cup to add exactly 2 cups of mashed mango into a separate, large bowl.
Add in 4 cups of granulated sugar and stir until the sugar is fully incorporated.
Set a timer for 20 minutes and let the mixture sit, stirring every few minutes to help the sugar dissolve.
Pour 3 Fl oz. or 1 pouch of liquid pectin into the mango mixture. Squeeze out every last drop of pectin! Fold the packet down as you go to get all of it out.
Add in 2 Tbsp of bottled lemon juice, then set your timer for 3 minutes and stir the mixture somewhat aggressively. I like to switch arms halfway through so that they don't feel like they're going to fall off.
Pour the mixture into the clean jars, leaving at least half an inch at the top of the container. The jam will expand as it freezes, so it's important to leave a little room!
Wipe away any spills, then close the jars with their lids and let them sit for 24 hours at room temperature. Place them in a safe area where they won't be touched or bumped.
Once the jam has set, place a bit of tape on each jar and write the date it was made.
Then either freeze or refrigerate the jam! It can be frozen for up to a year or kept in the fridge for up to a month.
To thaw frozen jam, move the container from the freezer to the fridge, then enjoy the following morning once it's thawed.