Wash whole mangoes thoroughly, submerge in room-temperature water for 30 minutes to cool, then dry completely with a clean towel. Chop into 1.5-inch cubes with the hard shell intact using an Avakaya cleaver. Remove inner seed and peel away the translucent white inner membrane from each piece. Air-dry cubes under a fan for 45 minutes until touch-dry.

Dry-toast fenugreek seeds in a skillet on low heat for 2-3 minutes until lightly golden; let cool and grind to fine powder. Grind raw, unroasted brown mustard seeds in short pulses until smooth. Grind sun-dried rock salt to a powder.

In a sterile, bone-dry wide basin, whisk together the mustard powder, chili powder, ground salt, toasted fenugreek powder, and turmeric powder until uniformly blended.

Dip dried mango pieces into a small bowl of sesame oil, transfer to the spice basin, and toss thoroughly until heavily coated. Mix in whole garlic cloves and pour in 250 ml of sesame oil, folding with a dry ladle until a thick, shiny, crumbly mixture forms.

Pack the coated mangoes into a sterilized ceramic crock or glass jar. Pour remaining sesame oil over the top to seal the surface. Cover with lid, tie a clean cotton cloth around the neck, and rest at room temperature in a dry pantry for 3 days.

On Day 3, unbind the jar and fold thoroughly with a bone-dry spoon from bottom to top. Taste for salinity—salt must slightly lead sourness (mix in 2 tablespoons salt if tartness dominates). Level the surface and confirm at least 0.5 inches of clear oil rests above the solids, adding warm-then-cooled sesame oil if needed. Reseal tightly.