Melt the butter in a large frypan over medium heat. Stir in the onion, mushrooms, and brown sugar. Cook and stir until the onion has cooked to a deep brown colour, about 10 minutes and set aside.
Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the gnocchi and return to a boil. Cook until the gnocchi floats to the top, about 3 minutes; drain, and keep warm.
Place the frypan over medium-high heat and stir in the prawns. Cook and stir until the prawns have turned pink on the outside and are no longer translucent in the centre, about 5 minutes. Add the onion mix, sour cream, paprika and saffron. Cook and stir until the mixture begins to simmer, then gently fold in the cooked gnocchi, then season to taste with salt.
Serve with grated basil and Parmesan cheese to serve.