Carefully remove stem from mushrooms and scrape gills from underside. Brush mushrooms with damp paper towel to remove any residual dirt. (See Tip 1)
Using a small paring knife, make shallow crosshatch cuts in the cap of mushrooms. Do not cut too deep. Place mushrooms, cap side up in a shallow dish. (See Tip 2)
To make the marinade, combine olive oil, balsamic vinegar, Worcestershire sauce, garlic, salt and pepper in a small bowl.
Spoon marinade over mushrooms. Allow mushrooms to marinate for 30 minutes to 1 hour, turning mushrooms half-way though.
Cook mushrooms in a panini press heated to 420° F for 6 to 8 minutes. Alternatively, cook mushrooms cap-side down in a skillet heated over medium-high heat or on a hot grill for 6 to 8 minutes; turn mushrooms and cook for an additional 6 to 8 minutes.
Serve on toasted hamburger buns with your favorite condiments.
Yield: 2 Portabella Mushroom Burgers. (See Tip 2)
Tips/Notes
If the stem doesn't come out easily, make a series of vertical cuts in it with a small paring knife. Remove sections of stem until all of the stem has been removed. Use a small spoon to carefully remove the gills. The reason that you want to remove the gills is that they will become unsightly and taste bitter when the mushrooms are cooked.
The crosshatch cuts in the mushrooms should not be any deeper than about 1/16 of an inch.
This recipe can be easily doubled for 4 to 6 Portabella Mushroom Burgers.