Beef heart of rump roast with boulangère potatoes

Ingredients

• 1.5kg Field & Flower Heart of Rump Roast
• 2 tsp English mustard powder
• 1 onion, roughly chopped
• 2 carrots, roughly chopped
• 2 sticks celery, roughly chopped
• 2 sprigs each of rosemary & thyme
• 300ml red wine
• 400ml beef stock
• 1 tbsp softened butter
• 1 tbsp plain flour
• 1 tsp Dijon mustard
• Olive oil
• 2 onions, thinly sliced
• 2 cloves garlic, crushed
• 1.5kg Maris Piper potatoes, peeled & sliced
• 2 sprigs fresh thyme, leaves picked
• 450ml TRUEfoods chicken stock
• 20g butter, cubed