Prepare potatoes. This recipe was intended for left over mashed potatoes. If you don't have those, bake two potatoes and then scoop out and take through a food mill or ricer. Add a knob of butter, salt and proceed with recipe.
While potatoes are cooling, prepare brussels sprouts. Shred with knife or mandolin. Remove large leaves and save those for garnishing the plate.
Saute shallots or onion in butter and olive oil until soft. Add brussels sprouts, fresh thyme cook for 5- minutes on medium heat.
Add brussels sprouts and cheese to potatoes. You want a ratio of about 1 to 2, brussels sprouts to potatoes. Add egg. Mix thoroughly. Add flour. Mix gently. Using floured hands and a clean cutting board that has been floured, roll into long tube. Cut and run fork across. Put in salted boiling water until they rise to top, about one minute only.
Remove from water, drain well.
Put butter into frying pan. Add sage leaves and fry leaves until crisp, not browned. Remove. Add gnocchi, and fry until golden brown. Serve immediately.
Pan fry in sage butter.