Ingredients

• 2 tablespoons butter, or as needed
• 1 pound beef oxtail, cut into pieces
• 1 onion, chopped
• 1/2 (750 milliliter) bottle red wine, or to taste
• water to cover
• 1 pound potatoes, peeled and cubed
• 2 carrots, chopped
• 2 ribs celery, chopped
• 1 cup green beans
• 1 (14.5 ounce) can stewed tomatoes
• salt and ground black pepper to taste

Instructions

1. Heat butter in a large skillet over medium heat. Add oxtail and onion; cook until oxtail is until browned, 5 to 7 minutes per side. Transfer oxtail and onion to a slow cooker.
2. Pour wine into the skillet and bring to a boil while scraping the browned bits of food off the bottom of the skillet with a wooden spoon. Pour wine mixture into slow cooker; add water to cover.
3. Set slow cooker to Low; cook soup for 8 hours. Add potatoes, carrots, celery, and green beans; cook soup for 4 hours more.
4. Cool soup slightly; refrigerate until fat has risen to top and solidified, about 1 hour. Scoop off fat; stir in tomatoes. Reheat soup on stove before serving.