1/2 cup (1 stick) unsalted butter
1 large or 2 medium-size yellow onions, chopped
1 quart home-canned tomatoes or one 28-ounce can imported Italian whole or chopped plum tomatoes, with their juice
1/2 cup dry vermouth or dry white wine
1 tablespoon sugar
1 heaping teaspoon dried tarragon
Kosher or sea salt to taste
Cold sour cream for serving
1) Melt butter in a large skillet set over medium heat. Add onion and cook until golden, about 15 minutes, stirring often to cook evenly.
2) Combine tomatoes, vermouth, sugar, and tarragon in a slow cooker. Scrape contents of skillet into tomato mixture.Cover and cook on LOW for 5 to 6 hours.
3) Purée in batches in a food processor or with a handheld immersion blender. Stain soup if you wish. Season with salt. Keep warm on LOW without letting it come to a boil until serving. Ladle hot soup into bowls and top with a spoonful of cold sour cream. Yield:4 servings.