Heat oven to 200C/180C fan/ gas 6. Remove the tough stems from the kale, then boil it in lightly salted water for 3-5 mins. Drain and press out the excess water.
Heat the butter in a frying pan and add the kale and garlic. Cook over a low-to-medium heat for a few mins. Season well and add some nutmeg.
Trim the broccoli and halve any thick stalks lengthways. Steam for 3-4 mins or until only just tender. Blot with a tea towel to get rid of the moisture on the surface.
Tip the kale into the base of a gratin or casserole dish and place the broccoli on top. Season well and grate over some nutmeg. Pour the cream over, then add both cheeses. Bake in the oven for 30-35 mins or until golden and bubbling.