Grind up the mustard seeds in your spice grinder to almost a powder but still with a little texture. Measure out 1 cup.
Peel the mangoes and cut chunks of the tender flesh off until you reach the grainy parts close to the seed. Put all the mango pieces into the food processor.
Peel the garlic and remove the stem and seeds from the habaneros and add them as well. Process until smooth.
Pour in the mustard seed and pulse a few times until well combined.
Allow to sit at room temp in the food processor for 15-20 minutes.
Finally add in the vinegar and salt and pulse until combined.
Add a few more splashes of vinegar if it seems too thick.
It will thicken slightly overnight but not much.
Pour into leftover mustard containers.
