Cut the leaves from the cauliflowers and set aside. Cut three thick “steaks” from the centre of each cauliflower, and break the rest into florets, keeping the stalks. Rub the slices, stalks, florets and leaves in oil, just enough lightly to coat them. Arrange the leaves, stalks and florets in a single layer in an oven tray and the slices in a second tray, then season sparingly.
Scoop two heaped tablespoons of the coconut solids from the tin of coconut milk into a wok, and fry on medium-high heat for 10 minutes, until the oils separate and the solids start turning golden. Turn down the heat, stir in the garlic, ginger, half the chilli and 10 curry leaves, and fry gently, stirring, for five minutes.
Roughly crush the fennel and cardamom seeds in a mortar and add to the wok with the turmeric, fish sauce, tamarind, tomatoes and the rest of the tin of coconut milk. Add 100ml water and leave to simmer on a low heat for 20 minutes, until the sauce has thickened.
Meanwhile, heat the grill to high and grill the tray of cauliflower leaves, stalks and florets for six to seven minutes, until slightly charred at the edges but retaining some bite, then tip into the curry sauce. Grill the cauliflower slices for 15 to 20 minutes, turning them halfway, until tender and lightly blackened. In a separate pan, fry the remaining curry leaves in the rest of the oil for three or four minutes, until crisp.
Divide the curry into six shallow bowls, and top each with a grilled cauliflower slice, some cashews and a scattering of fried curry leaves. Put the leftover chilli in a little bowl, for those who want an extra kick.