(Vegetarian) Cooking at home: Cauliflower au gratin

I was asked to do a recipe series for some vegetarian dishes for a local magazine recently. Given I am not a vegetarian myself, I found it a bit ironic but nonetheless I wanted to take this up as a challenge, to come up with something decent yet easy to make for fellow home cooks. At the end I made a 4-course dinner with salad, pasta, main and dessert which can be done within one hour if you prepare some steps in advance - at least that was the plan.