Preheat the oven to 180˚C fan / 200˚C / 356℉ convection / 392℉.
In your casserole dish / Dutch oven, fry the sausages in the oil on a medium - high heat until golden on all sides - about 5 minutes, turning occasionally.
Remove the sausages from the pan to a plate and set aside. Add the chopped onion to the pan, fry over a medium heat for 5 minutes, stirring occasionally, until softened.
Add the grated carrot and cook for 3 minutes until starting to soften. If the carrots and onion are catching on the bottom of the pan, add a splash of water.
Make the sauce: In a small bowl whisk the Dijon mustard with the Worcestershire sauce, soy sauce, brown sugar, vinegar, tomato puree and cornflour, then add the water and whisk to combine.
Chop the sausages into thirds, then add back into the pan with the carrot, grated apple and sauce.
Stir, then cover with the lid and place in the preheated oven for 30 minutes, until the sausages are tender and the sauce has thickened.
Serve straight away with pasta, rice, or potatoes, or cool completely and store in the fridge for up to 3 days or freeze.