Jazzed Up Mashed Potatoes With Kale

Name: Jazzed Up Mashed Potatoes With Kale
Ingredients: 2 tablespoons butter; 1 large sweet onion,* chopped; 1 leek, cleaned and thinly sliced; 1 bunch kale,* leaves washed, pulled off of stem and chopped; 3 cloves of garlic, minced; 7 medium-sized potatoes* (2.5 lbs), scrubbed and cut into small cubes; 1 1/2 cups milk; 1/2 teaspoon salt; 1 teaspoon mustard; 1 cup walnut pieces; 1 crispy apple,* with peel on, cut into small pieces; 1 cup cheese (gouda, edam, cheddar or monterey pepper, to taste; freshly ground nutmeg, to taste; sausage or vegetarian sausage (optional)