Lentil Shepherd's Pie

To quote Good Housekeeping's Vegetarian Meals cookbook: "A steaming skillet of Indian-spiced lentils are topped with piping-hot curried mashed potatoes for this nonmeat takeoff of an old comfort-food favorite." Some of you may be skeptical (not me, though, due to my love of all things sweet potato and lentil) but try it--just try it :) The recipe said to serve with yogurt, which I didn't have, so I used sour cream instead and that just put this dish over-the-moon. Move over old-school Sheperd's Pie, there's a new kid in town...
Lentil Shepherd's Pie
1 cup dry lentils, rinsed
1 Tbsp grated, peeled fresh ginger
1 tsp ground cumin
1 can (14.5 oz) vegetable broth
1 bay leaf
2 cups water
1 Tbsp olive oil
1 tsp curry powder
1/8 tsp crushed red pepper
3 large sweet potatoes, peeled and cut into 1-inch pieces
1 tsp salt
2 green onions, trimmed and thinly sliced
plain yogurt (or sour cream)

1. In 12-inch skillet, combine lentils, ginger, cumin, broth, bay leaf, and 1 1/4 cups water. Heat to boiling over high heat. Reduce heat to medium; cover and cook until lentils are tender, about 20 minutes. Discard bay leaf.
2. Meanwhile, in 3-quart saucepan, heat oil over medium-high heat. Add curry powder and red pepper and cook, stirring, 15 seconds. Add sweet potatoes, salt and remaining 3/4 cup water. Heat to boiling. Reduce heat to medium-low; cover and cook, stirring occasionally, until potatoes are tender, about 15 minutes.
3. With potato masher or fork, mash potato mixture until almost smooth. Spoon mashed potatoes over lentil mixture in skillet; sprinkle with green onions. Serve with yogurt, if desired.