In a roasting tray, place 2 carrots, onion and garlic on the base. Keep aside.
Heat a sauté pan over hight heat, drizzle some oil and add the striploin roast. Sear on all sides for 2-3 minutes until well coloured. Remove from the heat and place on the roasting tray.
Spread 2 tbsp of mustard over the joint and sprinkle a generous amount of cracked black pepper over and some salt.
Transfer in the oven, and roast for 55-60 minutes. ( 20 minutes per 500g, plus 10-15 minutes) Remove the joint from the oven & set it on a board covered with a tent of foil and allow to rest for at least 10 minutes.
Drain any excess fat from the roasting tray and place the tray back on the hob over medium direct heat.
Add in the flour and stir with a wooden spoon until the mixture becomes dry and lumpy in consistency. Pour in the brandy, flambéed then add the stock, 1 tbsp mustard, and simmer for 2 minutes to concentrate the flavours, stirring to lift the caramelised bits from the roasting tray.
Remove from the heat and strain through a fine sieve in a jug. Keep aside.
In a small saucepan, over medium/low heat, melt the butter or some of the cooking fat and add the shallot, garlic, thyme and extra peppercorns, cook for 30 seconds.
Pour in the cooking juices and add the cream and bring back to simmer for a further 2-3 minutes or until coating the back of the spoon. Remove from the heat and keep warm until required.
Carve the rested striploin and serve with the peppercorn sauce and some braised red cabbage.