Sweet Potato, Carrot, Apple & Red Lentil Soup (Sandra)

1/4 c butter
2 lg sweet potatoes, peeled & chopped
3 lg carrots, peeled & chopped
1 apple, peeled & chopped
1 onion, chopped
1/2 c red lentils
1/2 tsp minced fresh ginger
1/2 tsp black pepper
1 tsp salt
1/2 tsp each: cumin, chili powder, paprika
4 c veg broth
plain yogurt for garnish

Melt butter in large heavy pot. Add chopped veggies & saute till softened. Stir in lentils, seasonongs & broth. Bring to a boil, then reduce heat, cover and simmer for 30 min. Puree soup until smooth. Serve with yougurt for garnish.