Cook the gnocchi in a large pan of boiling water according to pack instructions. Plunge the spinach into the same pan, then immediately drain through a colander and shake off any excess water.
Put the crème fraîche in a small ovenproof dish with the grated parmesan. Add the hot, drained gnocchi and spinach and give everything a good stir. Crumble the blue cheese over and season with ground pepper.
Slide the dish under a hot grill until the cheese is bubbling and golden. Serve immediately.