Preheat the oven to 180C/350F/Gas 4.
For the pork, season the meat with salt and freshly ground black pepper. Heat the olive oil in an ovenproof frying pan and sear the meal on all sides for 2-3 minutes, or until golden-brown.
Sprinkle the sage over the top, add the garlic cloves and cloves to the pan, then transfer to the oven for 8-10 minutes and cook until the pork is golden-brown and cooked through. (The pork is cooked when the juices run clear when the pork is pierced in the thickest part with a skewer.) Remove the pork from the pan and leave to rest on a warm plate.
Deglaze the frying pan with the lemon juice, scraping up the caramelised bits on the pan with a wooden spoon.
For the chutney, heat the butter and olive oil in a pan over a medium heat. When the butter is foaming, gently fry the onion oil for 3-4 minutes, or until softened. Stir in the mustard and sugar and cook for 5-6 minutes, or until the sugar is melted and the sauce is smooth.
To serve, place the pork on a serving plate, drizzle the lemon pan juices around the plate and spoon the chutney to the side.