Place bread cubes in a bowl. Add chopped dried mushrooms, a pinch of salt and pour lukewarm milk over the mixture. Combine well and set aside.
combine all together
Dice the onion and pancetta. Set a saucepan over medium-high heat. Add diced pancetta and onion and cook until golden - brown. Slice prunes on thin slices. Add to the saucepan. When it all smells amazing and has a lovely color, add cognac and remove from the heat. Stir well. Add the herbs, chopped thyme, chives and sage. Add the mix to the bowl with bread. Leave for it to cool down a bit.
Separate the egg yolk and egg white. Add the egg yolk to a cooled bread mixture and stir well. Whisk the egg white, until you get a soft peak. Fold the egg white gently into the bread mixture. Season to taste with salt and pepper. At this point you can bake your bread stuffing or use it to stuff meat roulade.
Preheat the oven to 175 °C / 350 °F. Place the bread stuffing into a small baking dish. Make a water bath. Carefully pour boiling water into the pan. Make sure to avoid spilling water. Fill the water until it's half of the height of your baking dish. Bake for 35 - 40 minutes in a water bath.