Heat oil in your casserole dish over a medium to high heat and brown the sausages - you don't need to fully cook them at this point, you just want some colour on the skins.
Take out the sausages and set aside on a plate, turn the heat down to medium then add the onion to the pan and cook for about 5 minutes until soft but not browned.
Add in the garlic and carrots and cook for another 2 minutes, then add in the tomato paste, bay and thyme leaves.
Pour in the tinned tomatoes and stock and bring to the boil, then return the sausages to the pan.
Cover with the lid, turn the heat to low and let simmer for 20 minutes.
Take off the lid, give it a good stir to make sure nothing is stuck to the bottom of the pan, add the beans then let it simmer on low with the lid off for 10 minutes, stirring occasionally.
Season to taste and serve with some veggies and potatoes, rice or crusty bread to mop up the sauce - I love this with creamy mashed potatoes and some peas or broccoli.