Wash and dry 6 lemons. Add water to the steel insert of your Instant pot and place a trivet in that. Add lemons to any oven-safe bowl and place it on top of the trivet. Pressure-cook the lemons for 15 minutes at high pressure.
In the meantime, roast the spice blend for grinding. Add mustard, fennel, and fenugreek seeds to a microwave-safe plate, and microwave in 30-second increments for 2-3 minutes, stirring in between. Cool for 5-10 minutes, then grind to a fine powder using a spice or coffee grinder.
Wait for the pressure to release naturally, then open the lid once the pin drops. Cut the lemons in half or quarters depending on your preference. Remove all the seeds and discard them.
Turn the Instant Pot on sauté mode. Heat oil and add the reserved mustard seeds. When mustard begins to splutter, add lemons, salt, sugar, and red chili powder. Stir well.
Continue to sauté for 4-5 minutes till the juices reduce to a jam-like consistency. Turn off the Instant Pot. Cool the pickle and transfer it to an airtight container.
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Notes
Lemons: Pick lemons of the same size for even cooking.
Spices: While toasting, watch the spices carefully so they don't burn.
Sugar: You can substitute brown sugar with jaggery powder to make this achar with unrefined sugar.
Sweetness: Adjust the sugar quantity after sauteing. If the achar tastes too tart, add another tablespoon or two more of brown sugar.
Spiciness: Add another teaspoon of Kashmiri red chili powder to give this pickle a kick.
Avoid bitterness: After pressure-cooking the lemons, remove all the seeds, then sauté them.
Storage: Always store pickles in a clean, dry glass container with an airtight lid to prolong shelf life.
Note: The nutrition facts below are my estimates. If you follow any diet plan, I recommend cross-checking with your preferred nutrition calculator.