Spinach Surprise

1 pkg. frozen chopped spinach
1/4 c. chopped onion
4 tbsps. butter
pinch of salt
1/2 c. sour cream
1 tsp. vinegar

Cook spinach with onion. Melt butter, add spinach, well drained and stir it. Then add salt and sour cream, and blend together. Finally stir in the vinegar and serve.