I love lamb neck fillet...it's my favourite cut of lamb. I always do it in the slow cooker. I cut the fillets in half,gently brown and put in the slow cooker with garlic and some middle Eastern spices...cumin,chilli,coriander. Just a tiny bit of stock. I'll marinate the fillets if I've got time. Start on high,then reduce to low for several hours. Lovely with garlicky pan fried aubergines and tomatoes.