Heat a drizzle of rapeseed oil with the herb butter in a heavy based pan and seal the whole rolled shoulder on all sides to brown.
Add vegetables, sauté in the juices for a few minutes before adding the beer along with a similar quantity of water. Add remaining ingredients and simmer gently for two and a half hours. As long as you have a close-fitting lid it should be fine but check from time to time and add a little water if it is getting dry.
To make herby dumplings: mix dry ingredients in a bowl. Add milk, mixing with a knife until the dough comes cleanly away from the sides of the bowl – similar to a scone dough.
When the lamb is cooked, lift out joint to rest prior to carving and place spoonfuls of dumpling mix on the surface of the gravy. Replace lid and steam for 10mins.
Lift off lid for a final 5mins. cooking.
Spoon the vegetables and sauce into heated bowls and top with a generous slice of lamb and a couple of doughballs for a delicious meal. If you like your gravy thicker then add a little slaked cornflour at the end of cooking and bring to boil to thicken.