Special equipment: a 7 1/2-inch round ovenproof dish
Preheat the oven to 350 degrees F. In a large saute pan over medium heat, fry the onions, garlic, and thyme in 2 tablespoons of the oil for about 10 minutes, until soft and starting to turn golden. Meanwhile, very finely slice the eggplant and zucchini crosswise (1/16-inch thick). Use a mandoline or the slicer on the side of a box grater if you have one. Slice the tomatoes into 1/8-inch thick slices.
Pour the onion-thyme mixture into the ovenproof dish and top with a few slices of the vegetables to make a flat surface. Arrange the rest of the sliced vegetables, alternating the colors, in a circular arrangement around the dish. Drizzle with the remaining 2 tablespoons oil and sprinkle with the salt. Bake for 35 to 40 minutes or until the vegetables are soft and golden on top. Serve warm or at room temperature.
This can be made 1 day in advance and eaten at room temperature or reheated in a 325 degree F oven at for 20 to 30 minutes.
"My Little French Kitchen" by Rachel Khoo. Copyright Chronicle Books 2014. Provided courtesy of Rachel Khoo. All rights reserved.