1. Cover unpeeled onions with hot water, bring to boil and remove from heat. When cool enough to handle, peel, scraping the root end. (Don’t cut them because they might fall apart.)
2. Cover onions with boiling water, adding 1/2 teaspoon salt for each 2 cups of water. Bring again to a boil, cover and cook until barely tender. Drain and reserve liquid.
3. Melt butter and blend in flour. Gradually add 3/4 cup onion liquid and the cream, stirring to incorporate with the flour and butter. Cook, stirring until thickened.
4. Heat raisins and sherry together and add to onions with the cream sauce. Season with salt and pepper to taste.