Guy Savoy’s Vegetable Gratin
This is a vegetable gratin, similar to Thomas Keller’s ratatouille, except the bottom layer is that of melted onions – a sweeter and less umami version. I found some freshly harvested salad onions (spring onions with big white bulb) at the farmer’s market yesterday but you can use any onion. Thinly slice couple of large onions, toss with 1 Tbsp olive oil, 1 tsp red wine vinegar, a pinch of salt and a pinch of sugar. Let rest while you heat the oven to 400 F. Put the onions in a large enough gratin dish such that the onions form a single layer. Cook for 20-25 minutes, turning the onions every 5 minutes. Let cool. You can fry the onions on stove top as well but I wanted to make a one pot dish.
Cut and layer vegetables (zucchini, eggplant and tomatoes) as in ratatouille dish. Brush top with vinaigrette and scatter thyme leaves. Bake in 250F oven for 1-1.5 hrs. If you are serving fresh made gratin, it is worth the effort to cut the vegetables thinly and brushing the top with olive oil every 30 minutes of baking. This allows the vegetables to become crisp.