Melt butter and heat olive oil in a large soup pot over medium-high heat.Add diced onions, garlic, sliced smoked sausage rounds, kale, salt, pepper, rosemary and thyme; stir to combine and cook for 8 minutes, stirring occasionally.Stir in potatoes.Add chicken broth and soy milk; bring to a boil.Reduce to a simmer and continue to cook for 10 to 12 minutes, or until potatoes are fully cooked and tender.Remove from heat.Taste for seasonings and adjust accordingly.Remove rosemary sprig.Ladle soup into bowls and serve.