Preheat your oven to 180C (350F). Grab a heavy based, oven safe casserole dish.
Place the dried sourdough bread cubes into a large mixing bowl and set aside.
Add 150g of butter to a heavy based saucepan (I use my Dutch Oven) and allow it to melt before adding the onions and garlic. Allow them to soften for a few minutes before you add the celery and then the apple.You don't want these to brown, just soften in the butter. Once they are soft, turn off the heat and allow them to sit for a few minutes while you move onto the next step. Add the eggs to the liquid stock and whisk them together in a batter jug set aside.
To the large bowl with the sourdough bread, add the herbs and salt and pepper, as well as the softened vegetable mixture.
Pour three quarters of the liquid stock and egg mix over the top of the vegetable mixture and then mix everything through the sourdough bread cubes until they are all well coated.
Tip the sourdough stuffing mix into a heavy based baked dish and spread it evenly in the dish. Pour over the remaining stock mixture.
Cut the remaining 75g of butter into small cubes and place evenly over the sourdough stuffing mixture.
Cover the dish with foil and place into a 180C (350F) oven for around 30 minutes. After 30 minutes, remove the foil and cook for a further 45 minutes to 1 hour or until the stuffing is golden and crunchy on top and the liquid is no longer bubbling underneath.
Allow the stuffing mix to cool slightly before serving.