Prawns with Feta

I remember whipping this dish up with these ingredients when we had some last minute guests drop by. It was unbelievably delicious.
1 small onion, finely chopped, ½ oz. of butter, 1 tbsp. of olive oil, 125 ml of dry white wine, 4 tomatoes, peeled, seeded and chopped, 1 clove of garlic, crushed, ¾ tsp. chopped fresh oregano, salt, freshly ground black pepper, 4 oz. of feta cheese, crumbled, 2 lbs. of uncooked prawns, peeled and deveined, 4 tbsp. of chopped fresh parsley. Sauté onion in butter and olive oil in a saucepan for 5 minutes. Add wine, tomatoes, garlic and oregano. Season. Bring to the boil then simmer until sauce thickens slightly. Add cheese, mix well, and then simmer for 10 minutes stirring occasionally. Add prawns and cook over moderate heat for 5 minutes or until tender. Do not overcook. Transfer to a serving dish, sprinkle with parsley. Serves 4 or 1 if you are me.