For the apple sauce, in a saucepan, bring 300ml/10½fl oz water, the sugar and lemon juice to the boil. Add the sliced apple and cook until soft.
Blend to a purée using a hand-held blender, then pass through a sieve and leave at room temperature.
For the Scotch eggs, gently fry the onions in a little butter until soft but not coloured. Set aside to cool.
In a bowl combine the venison mince, pork belly mince, thyme, cooled onions, garlic, mace, juniper, salt and pepper. Divide the mixture into 85g/3oz balls. Press your thumb into the middle of each ball to make a hole. Push a quails’ eggs into each hole, then push the mince over the top to encase the quails' egg. Place on a baking tray and transfer to the fridge to chill.
Preheat a deep-fat fryer to 180C/350F and preheat the oven to 180C/350F/Gas 4 (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Put the beaten eggs, flour and breadcrumbs in separate bowls. Roll the Scotch eggs into the flour, patting off any excess. Coat the Scotch egg fully in beaten egg, letting any excess drip off. Finally roll the Scotch eggs in breadcrumbs until fully covered.
Gently place the Scotch eggs into the basket of the deep-fat fryer and lower into the fat. Cook until golden-brown (approximately five minutes). Carefully remove with a slotted spoon and transfer to a plate lined with kitchen roll.
Transfer to the oven for three minutes to ensure the meat is cooked and the egg is warm and still beautifully runny. Remove from the oven sprinkle with a little salt and serve with the apple sauce.