A hearty, stress-free supper that makes the best of leftover beef.
Preheat the oven to 180C/350F/Gas 4
Melt the butter in a frying pan and fry the onions for 15 minutes.
Sprinkle the onions with the flour and cook for two to three minutes. Season well with salt and freshly ground black pepper and set aside.
Fill the bottom of a baking dish with the onion, top with a layer of cooked beef and then tomato slices. Repeat the layering process until all the onions and beef are used up, finishing with the tomatoes on top. Pour over the stock until it fills half way up the dish.
For the gratin topping, mix the breadcrumbs, parmesan, olive oil and white wine together in a bowl until well combined. Season to taste with salt and freshly ground black pepper and then sprinkle this on top of the layered beef.
Bake for 20-25 minutes, or until crisp and golden-brown.
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