Preheat the oven to 190°C fan or Gas Mark 6.

Put the sausages, apples, onions and rosemary into a heavy flameproof casserole dish, in which the ingredients can lie in a single layer. There should not be a lot of space around the ingredients as the juices will reduce and burn. 

In a small bowl, mix the maple syrup, mustard, olive oil and garlic, then pour this mixture into the pan. Season and turn the ingredients to coat them in the syrupy mixture. Bake for 40-50 minutes, turning the sausages once. Sausages should be dark and the apples completely soft. 

Remove the dish from the oven and place over a medium-high heat, pouring in the stock. Bring almost to the boil, stirring to help the syrup and mustard mixture to amalgamate with the stock.

Add the blackberries to heat through and do not stir. 

For the olive-oil mashed potatoes:

Boil the potatoes whole in salted water until soft. Drain, reserving about half a cup of the cooking water.

Mash the potatoes and beat in the oil. Season to taste and add a little of the cooking water, enough to make a soft and slightly moist texture.

Stir in the spring onions and parsley. Serve with the baked sausages.