Preheat the oven to 180C/350F/Gas 4.
For the roasted grouse, heat a large oven-proof frying pan and add the oil. Once hot, add the grouse and fry on all sides to colour. Place in the oven for 15 minutes, or until the juices run clear. Set aside to rest in the pan.
Meanwhile cook the fondant potatoes. Cut the large potatoes in half widthways. Using a 3cm/1in diameter pastry cutter, cut two cylinders out of each potato.
Heat a deep, ovenproof saucepan and add a little vegetable oil. Place the potatoes in the pan standing on end and fry gently until golden-brown at the base.
Add the chicken stock to the pan and bring it up to the boil. Add the garlic, thyme and butter. Place in the oven for 20-30 minutes, or until the potatoes are tender.
For the redcurrant and bread sauce, stud the onion all over with the cloves and place into a saucepan, along with the bay leaf, peppercorns and milk. Bring the mixture to the boil, then remove the pan from the heat and set aside to cool for 15 minutes.
Remove the onion, bay leaf and peppercorns, and stir in the breadcrumbs. Return the pan to the heat and cook very gently for 5-10 minutes, stirring occasionally until the breadcrumbs have absorbed all the liquid. Stir in the butter and season, to taste, with salt and freshly ground black pepper.
Transfer the grouse to a warm plate and heat the pan. Add the balsamic vinegar and red wine. Stir to deglaze the pan, scraping up any brown bits from the bottom of the pan. Add the butter and redcurrants and bring to a simmer. Cook for a few minutes until the volume of liquid has reduced and thickened to a sauce consistency.
For the game chips and wild mushrooms, heat a frying pan and add the butter. Once melted, add the mushrooms and fry gently for three minutes.
Heat the vegetable oil in a deep, heavy-bottomed saucepan until a small cube of bread sizzles and turns golden-brown when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Deep-fry the potato slices for 1-2 minutes, or until crisp and golden-brown. Remove the game chips from the oil with a slotted spoon and set aside to drain on kitchen paper. Season with salt and freshly ground black pepper.
Just before serving remove the breasts from the grouse.
To serve, place the fondant potatoes in the centre of serving plates. Top with two grouse breasts per person and add the sautéd mushrooms. Drizzle with the redcurrant sauce and the bread sauce. Garnish with game chips.