Worcestershire sauce and mushrooms are rich in umami -- the savory flavor our brains associate with meat. We used both in our shepherd's pie, a low-fat, high-fiber, 'tater-topped casserole that delivers 100 percent of your daily comfort.
In a medium saucepan, bring 1 cup vegetable broth to boiling. Add lentils, rosemary and thyme, and simmer, covered, for 30 to 40 minutes or until tender. Drain any excess liquid; set aside.
Meanwhile, in a Dutch oven, bring 6 cups water to boiling. Add potatoes and garlic cloves; cook 15 minutes or until potatoes are tender. Drain, reserving 1/2 cup water. Coarsely mash with potato masher. Add 3 tablespoons butter and the salt; mix well. Add as much of the reserved water to make a fluffy mixture.
In a large oven-going skillet, heat 1 tablespoon butter over medium heat. Add mushrooms and onion and cook, stirring occasionally, for 10 minutes. Stir in peas and carrots.
In a small bowl stir together remaining 1 cup vegetable broth, the soy sauce, cornstarch and Worcestershire sauce; stir into mushroom mixture in skillet. Increase heat to medium-high. Cook and stir until mixture bubbles and thickens; cook 1 minute more. Stir in cooked lentils.
Top vegetable mixture with mashed potatoes, spreading to edges. Dot the top of the potatoes with the remaining 1 tablespoon butter. Bake at 375° about 20 minutes or until potatoes begin to brown.