Kumara, Potato and Cabbage Gratin
2 tablespoons olive oilsmall knob of butter2 large onions, thinly sliced3 cloves garlic, crushed2 teaspoons cumin seeds½ small cabbage, thickly sliced500 grams agria potatoes, peeled800 grams mixed kumara, peeled1 cup cream½ cup milk2 tablespoons Dijon mustard100 grams grated gruyere cheeseparmesan,...