BBC Food - Recipes - Beer-marinated rack of pork with Swiss-chard gratin

Ingredients

• 2 tbsp sea salt flakes
• 2 tbsp dark brown sugar
• 1 tsp black pepper corns
• 4 garlic cloves, lightly crushed
• 2 bay leaves
• 2 tbsp yellow mustard seeds , 1 tbsp soaked in cold water overnight
• 4 sprigs fresh thyme
• 4 sprigs fresh flatleaf parsley
• 500ml/18fl oz beer , preferably a good-quality ale
• 1 x 1-1.2kg/2lb 4oz-2lb 10oz six-rib pork loin rack, French-trimmed (ask your butcher to do this for you)
• 75g/2½oz unsalted butter
• 100g/3½oz brioche , roughly torn
• 1 tsp English mustard powder
• 1 tbsp brown mustard seeds , soaked in water overnight
• 700g/1lb 9oz Swiss chard , trimmed, chopped into 2cm/¾in slices
• 2 large potatoes , peeled and cut into 1.5cm/½in pieces
• 1 onion , sliced
• 50g/1¾oz unsalted butter
• 50g/1¾oz plain flour
• 400ml/14fl oz full-fat milk
• 200ml/7fl oz chicken stock
• 100g/3½oz Gruyère , grated
• salt and freshly ground black pepper