sliced 1 onion -- sliced salt and pepper 3 cups milk 3 Tbsp. butter 3 Tbsp. flour 1. Cook the celery, potatoes and onions in just enough water to cover them; until tneder. 2) Combine the milk and the flour, stirring out the lumps, and then add to the vegeatbles stirring until mixture has thickened. 3) Season with salt and pepper, and then melt the butter on top.