In a saucepan melt butter add onion and garlic and cook on low just to soften, do not brown, whisk in flour and cook on low 2 minutes, whisk in chicken stock and cream and all seasonings except cheese, stir and simmer until thickened, add cheese on low to melt, taste to see if salt, pepper or more lemon is needed. Add reserved potatos and heat through, Transfer hot to serving dish.