For the lamb, preheat the oven to 220C/425F/Gas 7.
Season the lamb loin all ove with salt and freshly ground black peppe, to taste
Heat the lactose free butter and oil in an ovenproof frying pan over a medium heat. Add the seasoned lamb and fry for 6-8 minutes, turning regularly, until browned on all sides.
Add the star anise and thyme, then transfer the pan to the oven and cook for 7-8 minutes (for medium), or until cooked to your liking. Remove from the oven and set the lamb aside on a warm plate to rest for 10 minutes. Reserve the pan juices in the pan.
Meanwhile, add the chicken stock to the pan the lamb was cooked in and bring to a simmer, scraping up any browned bits from the bottom of the pan using a wooden spoon, to deglaze. Continue to simmer until the volume of liquid has reduced by half and the pan juices have thickened. Season, to taste, with salt and freshly ground black pepper. Set aside and keep warm.
For the sautéed pumpkin, heat the butter and olive oil in a frying pan over a medium heat.
Add the star anise, thyme and cubed pumpkin and fry, stirring regularly, for 4-5 minutes, or until the pumpkin cubes are tender and golden-brown. Remove the star anise and discard (or rinse and save for another recipe).