1. Cut the potatoes and cauliflower, removing the stems (keep the florets), then cook in boiling water for 15 minutes - drain.
2. Spread the cauliflower in a gratin dish with the ham cut into strips. Whisk the egg with the soy milk - season with salt and pepper and pour over the cauliflower.
3. Sprinkle with a little gruyère and parmesan cheese and bake at 210°C for about twenty minutes.
4. For a lactose-free version, replace the cheese with gluten-free breadcrumbs.