Preheat oven to 350 degrees. Use a 9-inch square (2-3 qt.) glass pan or casserole dish, at least three inches deep.

1. Heat 1/3 cup of oil in a heavy-bottomed pan or casserole. Add the chopped onions and carrots. Simmer over medium heat, stirring, for approximately 8-10 minutes until the onions begin to look transparent. Add bay leaf, Turmeric, coriander, and a half teaspoon each of salt and pepper. Stir and simmer over low heat until onions are gooey and tender, golden but not burnt, about 10 to 15 minutes more. 
2. Meanwhile, steam the broccoli and cauliflower until just tender; do not overcook. Combine in a large bowl, adding a pinch of salt and pepper. 
3. Spread half of the onion mixture in the bottom of the baking pan. Add half the vegetable mixture, then top with half the grated cheddar cheese. Repeat, with the rest of the onions, then vegetables and remaining cheese.
4. Drizzle all over with the ½ cup of broth. Season lightly with salt and pepper.
5. For the topping, in a small bowl combine the melted butter, Panko, parmesan and a few grinds of black pepper until well blended.
6. Sprinkle the topping evenly on top of the casserole.
7. Bake for 25 minutes in a 350-degree oven until the casserole light golden brown on top and bubbling.