Pre-heat the oven to 190°C / 170°C fan assisted / gas mark 5 / 375°F and line a roasting tin with baking parchment.
Prepare the apples by peeling, coring and slicing. Add them into a small bowl with the lemon juice and stir to coat. Set aside until ready to make the caramelised apples.
To caramelise the onions for the gravy heat the pan for a couple of minutes on a medium heat. When hot, add 20g of the butter plus the olive oil.
Add the onion slices and heat on medium-low heat for about 20-25 minutes until sticky and caramelised. Stir the pan occasionally to collect all the brown sticky bits from the bottom.
Whilst the onions are caramelising, peel and quarter the potatoes. Place them into a large pan of cold water and bring up to the boil. Once boiling, set the timer for 20 minutes until tender.
Also place the sausages in the roasting tin and roast for 25-30 minutes until the sausages are golden and juicy.
Meanwhile continue making the onion gravy. For the end 5-10 minutes of the onions cooking you will be stirring almost continually to avoid the catching onion burning. The onions are ready when they are still soft but golden and sticky.
Turn the heat to low and pour in the apple cider vinegar and stir well to deglaze the pan.
Add the herbs and the salt and pepper.
Stir in the butter until melted then add the cassava flour. Switch to a whisk and mix the flour in well until it has all been absorbed by the fat.
Pour in the stock very slowly, about 100ml at a time, stirring continually to remove lumps until it gradually begins to resemble a sauce. Once about half of the stock has been added you can turn the heat up to medium and keep on stirring in the stock until it has all been added.
Pour in the apple cider and whisk in until smooth and the only lumps in the gravy are the onion.
Whisk in the dijon and the worcestershire sauce and bring the gravy up to a gentle boil.
Turn the heat down and simmer for at least 10 minutes and place on a very low heat until ready to serve.
Once the potatoes are ready, drain them and then pass them through a potato ricer into a large mixing bowl.
Make the brown butter for the potatoes by placing the butter in a saucepan over medium heat. Listen for hissing and cracking sounds as the butter melts and watch for little brown bits forming at the bottom of the pan. Once the noises subside, the butter smells toasty, and is just starting to turn brown, remove from heat immediately and pour into a small heatproof bowl to avoid further cooking and burning.
Pour the milk into the browned butter to warm up.
Stir the brown butter and milk into the mashed potato using a silicone spoon and season with the salt and pepper.
Make the caramelised apples. Melt the butter in a large frying pan then add the icing sugar and salt. Then add the apple slices.
Fry for about 5 minutes until the apples are just softening and beginning to colour then remove from heat.