Pre-heat your oven to 200℃ (390℉). Line a large oven tray with baking paper.
Cut the top off a large loaf of bread (see what I've written in the main post) and carve out the bread (save it to make breadcrumbs), to create a deep trench. Make sure you leave about 2cm (¾ inch) in the bottom.
Melt the butter and add the garlic. Brush over the insides of the loaf.
Add as much cheese as you like to fill the bottom (I didn't measure it, but went by how much it took to fill the hole).
Spoon over your cooled mushroom bolognese, just until it reaches the top of the hole (I had the perfect amount of sauce).
Sprinkle over as much mozzarella as you like (again, I didn't measure it, and just eyeballed it).
Bake just until the cheese is bubbling and brown (around 10-15 minutes). Slice and enjoy with a tasty salad!