Preheat the oven to 350°. In a bowl, mix together all three cheeses. Lightly brush a 7-quart, enameled cast-iron casserole with olive oil. Arrange one slightly overlapping layer of potatoes in it followed by one layer of the cauliflower (including the crumbles) . Scatter some of the onion on top and sprinkle with 3/4 cup of the cheese. Drizzle with 1/2 cup of the <em>vadouvan</em> cream. Repeat this layering 3 more times with the remaining potatoes, cauliflower, onion, cheese and cream. Pour the remaining cream mixture all over the top.