- 4 large portobello mushroom caps, gills scraped
- 2 tablespoons extra virgin olive oil (EVOO), plus more for brushing
- Salt and pepper
- 1 pound ground beef, at room temperature
- 1 small onion, chopped
- 2-3 cloves garlic, chopped
- 3 tablespoons Worcestershire sauce
- 1 teaspoon dried marjoram or oregano
- 1 cup watercress, chopped and packed
- 1/2-3/4 cup panko breadcrumbs
- 1/2 cup grated Pecorino Romano cheese
- 1 1/2 cups shredded provolone cheese
Pre-heat the oven to 425°F.
On a rimmed baking sheet, brush the mushrooms with EVOO and season with salt and pepper; situate them rounded-side up. Roast until softened, 8-10 minutes.
Meanwhile, in a large skillet, heat 2 tablespoons EVOO, two turns of the pan, over medium-high heat. Pat the beef dry and add it to the skillet; season with salt and pepper. Cook, stirring, until browned, about 5 minutes. Add the onion, garlic, Worcestershire sauce and marjoram (or oregano). Cook until the onion and garlic are softened, about 5 minutes. Add the watercress to wilt. Stir in the panko. Remove the pan from the heat; stir in the Pecorino Romano.
Flip the mushroom caps over so they're rounded-side down and fill them with the meat mixture, mounding a quarter of the beef into each cap. Top with the provolone and return to the oven to melt the cheese, 7-8 minutes.