Portabello Burgers with Watercress Pesto
Vegetarians and non-vegetarians alike will love these burgers, topped with a flavorful watercress pesto.
- 1/2 cup balsamic vinegar
- 3-4 sprigs rosemary
- 1/4 cup Worcestershire sauce
- 1/2 cup extra virgin olive oil (EVOO), divided, plus additional for drizzling
- 4 large portabello mushroom caps
- 2 medium tomatoes, cut into 1/2-inch-thick slices
- Salt and freshly ground black pepper
- 4 slices provolone cheese
- 4 thick-cut slices Italian bread
- 2 cups watercress
- 3 tablespoons walnuts, toasted
- Juice of 1 lemon
- 2 cloves garlic, 1 left whole and 1 chopped, divided
- Pre-heat the oven to 275ºF.
- In a large mixing bowl, combine the balsamic vinegar, rosemary, Worcestershire sauce and 1/4 cup EVOO (eyeball it). Add the mushroom caps to the bowl and toss to coat. Marinate in the refrigerator for several hours.
- While the portabellos are marinating, arrange the tomato slices on a baking sheet and drizzle them with a little EVOO and a sprinkle of salt and pepper. Roast them in the oven for 1 hour, then turn the oven up to 325ºF for another 30 minutes until the tomatoes are light golden brown; reserve.
- When you’re ready to cook the burgers, pre-heat a grill pan over medium heat. Remove the mushrooms from the marinade, blotting off any excess with a paper towel. Season them with salt and pepper, and grill until grill-marked and tender, about 3 minutes per side. When you flip them, lay down a slice of cheese on each one to melt.
- When the mushrooms are getting close to finishing up, place the bread slices on the grill as well and cook until charred, about 1 minute per side. When the bread slices come off the grill, rub them with the whole garlic clove and give them a drizzle of EVOO and a sprinkle of salt and pepper.
- While the mushrooms and bread are grilling, set up a food processor. In the bowl, combine the watercress, walnuts, lemon juice, chopped garlic, and some salt and pepper. Pulse the machine a few times to chop everything up, then turn on the machine and stream in the remaining 1/4 cup EVOO until it forms a smooth pesto.
- To assemble each burger, place a grilled mushroom cap, a couple slices of roasted tomatoes and a good dollop of pesto between two slices of grilled bread.