Combine the bread flour, yeast, and salt in the bowl of your stand mixer.
Add the water and using the dough hook attachment, mix on the lowest setting for 4-5 minutes until the dough is smooth and pliable. If the dough sticks to your fingers, add a bit more flour
Cover the dough with cling film and leave to proof at room temperature for an hour and a half, or until doubled in size.
Give the dough a punch, or knock it back if you will, and then transfer the dough to a floured work surface. Knead the dough for a minute to get any other pockets of gas out then cut off a third of the dough.
Shape the smaller and larger pieces of dough into their own respective balls and place each piece on a greased baking tray. Leave room between the two pieces and then cover and leave to proof for another 30-40 minutes until doubled in size,
While the dough is on its second proof, preheat the oven to 450 deg F and place the second metal tray in the bottom of the oven
Uncover the dough and flatten the tops of each piece slightly. Place the smaller loaf on top of the larger loaf.
Dip your fingers in flour, and using your thumb and index finger, or your middle and ring finger if you're feeling naughty, push into the middle of the loaf to join the two pieces together.
Leave the loaf to proof for another ten minutes and brush with the egg to glaze.
Score the dough using a razor or sharp knife. Don't be afraid to cut into the dough a bit, scoring give the dough a place to expand and you want it to be on the sides of the loaf, not the middle.