Pressure cooker lamb karahi with new potatoes

Name: Pressure cooker lamb karahi with new potatoes
Ingredients: 1kg/2lb 4oz lamb leg, cut into 4cm/1½in pieces; 6 garlic cloves, peeled; 5cm/2in piece fresh root ginger, peeled; 1 tsp salt; ½ tsp freshly ground black pepper; 4 tbsp sunflower or vegetable oil; 1 large brown onion (or 2 small), finely chopped; 1 tsp chilli powder; 2 tsp ground coriander; 1 tsp ground turmeric; 1 tsp ground cumin; ½ tsp garam masala; ½ tsp ground fenugreek; 500g/1lb 2oz baby new potatoes; 2 green chillies, 1 whole and 1 thinly sliced; 6 tbsp Greek-style yoghurt; cooked basmati rice; 5cm/2in piece fresh root ginger, peeled and cut into fine julienne slivers; small bunch fresh coriander