1. Prepare the cauliflower, separate all the florets and cut the larger pieces of stalk into small pieces.
Cook in a large saucepan of boiling salted water for 10 minutes with the bicarbonate of soda; drain well.
2. Place the rice in a fairly small saucepan with 12 fl oz (350 ml) water and scant 1/4 tsp salt. Once the water has come to the boil, cover the pan and cook over a low heat for 15 minutes by which time the rice should be tender and should have absorbed all the water.
3. Stir in scant 1 oz (20 g) of the butter and 3 tbsp of the grated cheese. Add a little more salt if wished.
Preheat the oven to 400°F (200°C) mark 6.
4. Make the bechamel sauce and season with salt, pepper and a pinch of nutmeg. Stir in 3 tbsp of the grated cheese.
5. Grease a gratin dish or any shallow, ovenproof dish with butter and spread the rice out in it evenly. Cover with a layer of the cauliflower; combine the two without breaking up the cauliflower too much and completely cover with the bechamel sauce.
6. Sprinkle the remaining cheese over the surface and dot with the remaining butter in small flakes.
7. Place in the oven for 15 minutes, after which the surface should be crisp and golden brown.