Preheat the oven to 180oC/Gas Mark 4. In a non-stick frying pan, melt the butter and add the onions, rosemary and thyme. Cook to soften the onions. Just before you take off the heat, add the chopped garlic cloves and soften. Empty into a bowl to cool.
In another large bowl, add the pork mince and egg. Beat the mixture (best done with hands) to work the egg into the meat, thickening it.
Add the onion mix and the diced apple to the pork mince, then combine with the rest of the ingredients. Season with salt and pepper.
Place the mix in a lined loaf tin and roast for 45 minutes, or until fully cooked through. Turn out onto a board and garnish with chopped walnuts, orange zest and thyme leaves.