I melt the butter in a pan over medium heat, then cook sliced onion until soft, about 5 minutes. I add the diced apple and continue to sauté briefly until it softens but still holds shape.
Once cooled slightly, I mix the cooked onion & apple into the sausage meat. Then I stir in chopped sage, breadcrumbs, salt and pepper, ensuring even distribution.
You can either spoon this mixture inside the turkey cavity (if safe and temperature allows) or transfer it into a greased loaf tin or baking dish. I top it with extra sage leaves and bake for about 30–40 minutes until golden and cooked through.