Filling
1/2 cup lentils
1/4 teaspoon salt
1 ounce dried porcini mushrooms
2 tablespoons olive oil, divided
6 ounces fresh mushrooms, sliced
1 medium onion, chopped
1 carrot, cut into 1/4-inch-thick rounds
1 1/2 teaspoons dried sage
1/4 teaspoon dried thyme
1 large garlic clove, minced
2 tablespoons all purpose flour
2 medium Yukon Gold potatoes, peeled, cut into 1/2-inch chunks
4 teaspoons soy sauce
1 tablespoon tomato paste
Topping
1 cup plus 2 tablespoons all purpose flour
6 tablespoons yellow cornmeal
1 1/4 teaspoons baking powder
1/2 teaspoon salt
4 tablespoons chilled unsalted butter, diced
1/2 cup buttermilk
3/4 cup (packed) coarsely grated Gouda cheese (about 3 ounces)Filling:
Combine 3 cups cold water, lentils, and 1/4 teaspoon salt in medium saucepan; bring to boil. Reduce heat, cover, and simmer until lentils are tender, 25 to 30 minutes. Drain; set lentils aside.
Pour 3 cups boiling water over porcini in medium bowl; soak 25 minutes. Remove porcini from soaking liquid, squeeze dry, and chop coarsely. (Reserve soaking liquid.)
Heat 1 tablespoon oil in heavy large skillet over medium-high heat. Add fresh mushrooms. Sauté 3 minutes. Add 1 tablespoon oil, onion, carrot, sage, and thyme. Sauté 4 minutes. Add garlic; sauté 30 seconds. Reduce heat to medium-low. Mix flour into vegetables; cook 1 minute. Add porcini soaking liquid. Mix in porcini, potatoes, soy sauce, and tomato paste. Cover; simmer until potatoes are tender, stirring occasionally, 13 to 15 minutes. Add lentils; season with salt and pepper. Divide filling among four 2-cup ovenproof bowls. DO AHEAD Can be made 2 days ahead. Cover; chill. Bring to room temperature before continuing.
Topping:
Preheat oven to 400°F. Combine flour, cornmeal, baking powder, and salt in processor; blend 5 seconds. Add butter; pulse until mixture resembles coarse meal. Add buttermilk; pulse until dough forms moist clumps. Turn dough out onto lightly floured surface. Divide into 4 equal pieces; shape each into 2/3-inch-thick disk. Set rounds atop filling; top with cheese.
Bake pot pies on baking sheet until tester inserted into biscuit topping comes out clean, about 30 minutes.