Turn your oven to a holding temperature of 140⁰C/gas mark 1. Trim any sinew and connective tissue away from the livers and cut them into even 4cm pieces. Pop them onto a piece of kitchen towel to blot away any blood – the drier they are, the better they colour in the pan.
Mix the eggs and milk together in a small shallow dish or tray snug enough to just fit the bread. Season generously with salt, pepper and a grating of nutmeg. Sit the bread in the mix and leave it to soak for 15 mins, turning halfway through.
Meanwhile, cook your mushrooms. Heat 1 tbsp of oil in a large frying pan. When very hot, throw in the mushrooms with a pinch of salt. Sauté for 10 minutes or so, until nicely coloured and darkened. Throw in the garlic and a knob of butter and cook for a final 2 minutes before removing from the heat and adding parsley and a squeeze of lemon to finish. Keep in the warm oven while you fry the bread.
Put a fresh frying pan on a medium heat and throw in a knob of butter. When it has started to foam add the soaked bread and fry for 3-4 minutes until golden brown on the undersides. Flip them over and cook until golden on the other side too. Slide them into the oven to stay warm alongside your mushrooms.
Give the frying pan a wipe clean and pop it on a very high heat. Season the livers generously with salt and pepper. Add a knob of butter to the pan and throw in the livers. Fry for 1-2 minutes until nicely coloured, then flip them over and cook for a final 1 minute on the other side. As you flip them add the sage leaves to the pan, so they have time to crisp up. Remove the pan from the heat and add a little glug of balsamic vinegar to finish and glaze.
To serve, divide the bread between two plates and top them evenly with the mushrooms, livers and sage. Serve with a wedge of lemon on the side.