Prepare the Ingredients: Peel and slice the onions, leeks, and shallots. Dice the Yukon Gold potatoes.
Caramelize the Onions: Caramelize the onions in a fry pan for faster results, then do the same with the leeks and shallots.
Cook the Soup: Combine caramelized onions, leeks, shallots, garlic, thyme, and diced potatoes in a large pot. Add beef, chicken, and vegetable stocks. Season with salt and pepper. Bring to a boil, then simmer for about 1.5 hours until the potatoes are soft.
Blend the Soup: Use an immersion blender to puree the soup until smooth. Adjust the texture with additional stock if necessary.
Finish with Cream and Alcohol: Stir in the ruby port wine, Harveys Bristol Cream sherry, and heavy whipping cream. Adjust the seasoning with salt and pepper to taste.
Serve: Serve hot, garnished with croutons or a sprinkle of fresh herbs if desired.