Peel and slice the shallots and garlic, then cut the cauliflower into florets.
Heat some oil in a pan and fry most of the shallots and the garlic until soft, then add most of the curry leaves and half the mustard seeds, crumble in the chilli and fry for 2 minutes.
Add the cauliflower, split peas and coconut milk, then fill 1 empty tin with water and add to the pan. Season, bring to the boil, then lower the heat and simmer for 40 minutes, stirring occasionally. If the liquid reduces too much, add a splash of water.
Fry the remaining shallots in oil on a high heat until crisp, then add the remaining curry leaves and mustard seeds and fry for 1 minute. Serve dhal scattered with the crisp shallot mixture.