Preheat the oven to 180C/gas 4. Prepare the bread bowl. Slice across the loaf of bread to remove the upper third then use your hands to pull out as much of the middle of the remaining loaf as you can, creating a crusty bowl. You won't need this excavated bread for this recipe, so set it aside to make breadcrumbs.
Bake the bread bowl for 10 minutes. Once it's cool enough to handle, gently rub the cut sides of garlic around the inside of the loaf. Coat the inside with mustard use the back of a spoon or even better, a pastry brush, to help you spread it evenly. Set the hollowed-out loaf aside and increase the oven temperature to 200C/gas 6.
To make the filling, toss the leeks with the olive oil, salt, pepper and thyme and roast for 30 minutes, or until meltingly soft. Leave to cool, then drain off any excess oil.
In a separate jug, make the custard by whisking together the eggs and cream, then season well with salt and pepper.
To assemble the loaf, place the bread bowl on a baking tray and spread the goats' cheese evenly on the base, then top with leeks. Pour the custard mixture into the bread bowl in three stages, waiting a few minutes each time before adding more. Once all the custard is added, carefully transfer to the oven. Bake for 10 minutes, then reduce the temperature to 170C/gas 3 and bake for a further 25-35 minutes until the custard is set. Check the custard is cooked by inserting a skewer into the middle
if it comes out wet, give it another 5-10 minutes. Leave it to cool for 45 minutes to 1 hour. It should look similar to a quiche, and you can slice it up to serve it in just the same way.
