- Preheat oven to 175C. In a food processor, blitz the onions, shallots and garlic in batches until coarsely chopped, then transfer to a bowl.
- In a frypan, heat the high-heat oil until it shimmers, then saute the onion mixture, stirring often until golden. Grind the fenugreek seeds, then stir through the onion mixture. Add the remaining ingredients, together with 1/2 tbsp of salt and 1/2 tsp black pepper.
- Spread a thin layer of the mixture on a parchment paper-lined baking sheet. Bake, stirring occasionally with chopsticks to separate onions, until well-browned and barely moist, approximately 30-45 minutes. Store in the fridge for one month or freeze for no more than six months.