Add butter, bacon fat, mushrooms, fresh thyme, and shallots in a stockpot. Simmer for 8 minutes until the mushrooms release their juice. Then add the lemon juice and Worcestershire

Simmer until the juices have reduced by half. Add the chicken stock and simmer until reduced by ¼. Add the cream and bring to a low boil and cook for another 5 minutes

Remove from the heat and purée the soup with an immersion blender until smooth. Place back on the heat, bring to a low boil, and thicken with the slurry, stirring until it thickens; continue to stir on low for 5 minutes

Taste and add more chicken base if needed. Season with salt, pepper, and simmer and stir occasionally for 15 minutes