Trim visible fat from lamb, pat completely dry and cut into chunks.
Place the fat trimmings into a large skillet and cook until fat renders out, then discard the solids.
Add lamb, onions and garlic to the pan along with thyme, chives, salt and pepper and saute until onions are browned and lamb is seared. Toss mixture with the 1/4 cup flour.
Place vegetables in the bottom of a large crock pot.
Place floured lamb and onions on top of that.
Pour stock and Guinness stout over all.
Cover and cook on low for 8-10 hours or until vegetables and lamb are tender.