50g/1¾oz lactose free butter, plus extra for greasing
300g/10½oz gluten free white breadcrumbs
300g/10½oz wholegrain mustard
200ml/7fl oz water
3 free-range eggs
Remove the beef from the fridge and let it come to room temperature. Score the fat using a sharp knife and rub it all over with the oil and salt.
Preheat the oven to 220C/425F/Gas 7. To make the crust, melt the lactose free butter in a pan. Put the gluten free breadcrumbs in a large bowl and mix through the melted lactose free butter. Mix together the mustard and water in a small bowl.
Add the mustard mixture and the eggs, into the gluten free breadcrumbs, season with salt and freshly ground black pepper and mix everything together to make a paste.
Spread the paste evenly over the beef, leaving the ends uncovered. Cover the paste with a piece of well-greased tin foil. Place the carrots in a large roasting tray and sit the beef on top of them.
Add some water to the tin to avoid it from burning. Place the beef in the oven and immediately reduce the oven temperature to 200C/400F/Gas 6.
Cook the beef for two hours. Remove the foil and cook the beef for one more hour. Remove the beef from the oven and leave it to rest for at least 20 minutes, carve the rested beef and serve.