Preheat oven to 400°. In a Dutch oven, heat 1 tablespoon oil over medium heat. Add shiitake mushrooms and cook in batches until dark golden brown, 8-10 minutes; remove with a slotted spoon. Repeat with 1 Tbsp. oil and the portobello mushrooms., In same pan, heat 1 tablespoon oil over medium heat. Add onions; cook and stir 8-10 minutes or until tender. Add garlic and 1 teaspoon rosemary; cook 30 seconds longer. Stir in beer, 1 cup broth, bay leaves, vinegar, soy sauce and sauteed mushrooms., Bring to a boil. Reduce heat; simmer, uncovered, 10 minutes. In a small bowl, mix cornstarch and remaining broth until smooth; stir into mushroom mixture. Return to a boil, stirring constantly; cook and stir until thickened, 1-2 minutes. Remove and discard bay leaves; transfer mushroom mixture to 8 greased 8-oz. ramekins. Place on a rimmed baking sheet., Layer sweet potatoes in a circular pattern on top of each ramekin; brush with remaining oil and sprinkle with pepper, salt and additional rosemary. Bake, covered, until potatoes are tender, 20-25 minutes. Remove cover and bake until potatoes are lightly browned, 8-10 minutes. Let stand 5 minutes before serving.