Pour 4 cups chicken stock into your blender and set aside. Dice ½ onion, 1 yellow squash, and 5 cloves garlic. In a large, heavy-bottomed pot over medium-high heat, melt ¼ cup butter. Add the diced onion and yellow squash, cooking for 4-5 minutes until softened. Add the chopped garlic and stir for 1-2 more minutes until fragrant. Carefully transfer the sautéed vegetables to the blender with the chicken stock.
Add 1 pound ground turkey to the same pot still over medium-high heat. Sprinkle 2 teaspoons sage, 1 teaspoon paprika, 1 teaspoon oregano, 1 teaspoon salt, ⅛ teaspoon pepper, and 1 tablespoon Worcestershire sauce evenly over the meat. Cook for 5-7 minutes, breaking up the turkey with a spoon until browned and cooked through. The seasonings will create an authentic Italian sausage flavor.
While the turkey cooks, blend the chicken stock and sautéed vegetables until completely smooth. Pour this flavorful broth over the browned turkey. Add 8 small diced potatoes, 1 teaspoon oregano, and ½ teaspoon salt. Bring to a gentle boil and cook for 10 minutes until potatoes are tender.
Stir in the chopped kale and boil for 10 more minutes until the kale is tender. Remove the pot from heat and let it stop simmering completely - this is crucial for preventing curdling. Slowly stir in the Greek yogurt until melted and smooth, creating a beautifully creamy texture.