GRILLED STEAK SANDWICH WITH PORTOBELLOS, GRILLED ONIONS, AND FONTINA

Grilled Steak Sandwich with Portobellos, Grilled Onions, and Fontina image

The key to success with this sandwich is knowing which way to slice the flank steak: against the grain of the muscle fibers. Hey, Philly never had it so good.

Yield serves 4; makes 2 cups mayonnaise

Number Of Ingredients 20

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Ingredients

1 head garlic
2 shallots
Needles from 2 rosemary sprigs
1 bay leaf
1 cup plus 2 tablespoons extra-virgin olive oil
Sea salt and freshly ground black pepper
1 1/2 pounds flank steak, about 3/4 inch thick
3/4 cup mayonnaise
Juice of 1/2 lemon
2 tablespoons fresh or prepared grated horseradish
2 bunches coarsely chopped arugula
Sea salt and freshly ground black pepper
4 portobello mushrooms, stems removed
1 red onion, sliced
2 tablespoons balsamic vinegar
1/4 cup extra-virgin olive oil
Sea salt and freshly ground black pepper
1 loaf ciabatta bread, split horizontally
1/4 pound fontina cheese slices
1 bunch arugula

Steps:

Preheat the oven to 350°F. Roasting garlic and shallots brings out their incredible sweetness and only adds one quick cooking step. Peel off the outer layer of the garlic and shallot skins. Smash them open with the flat side of a knife to break up the cloves. Rip off a large piece of heavy-duty aluminum foil and put the garlic and shallots in the center. Toss in the rosemary and bay leaf and moisten with 2 tablespoons of the oil and 1 tablespoon of water. Wrap up the aluminum pouch, making sure it is sealed tightly so none of the liquid seeps out. Put the pouch in the oven for 20 minutes to steam and soften the garlic and shallots. Unwrap the aluminum and carefully pour any juices into a food processor. Peel the garlic cloves and shallots and toss them into the food processor along with the remaining 1 cup of oil. Season with salt and pepper and pulse until the mixture is well blended. Lay the steak in a shallow platter and pour the flavored oil on top. Cover and refrigerate for at least 2 hours or up to overnight, turning the steak over occasionally so both sides feel the love of the oil.
To make the arugula mayonnaise, combine the mayo, lemon juice, horseradish, and arugula in a food processor. Turn the machine on for 1 minute to combine all the ingredients; the mayo will have a bright green color. Season with salt and pepper, cover, and pop it in the refrigerator.
Lay the mushrooms and onion slices in a shallow platter, drizzle with the vinegar and oil, and season with salt and pepper. Try not to break up the onion slices into rings, they are easier to grill as slices. Take the steak, mushrooms, and onions outside because we're about to make some magic.
Preheat your grill until it's very hot. Take a few paper towels and fold them several times to make a thick square. Blot a small amount of oil on the paper towel and then carefully and quickly wipe the hot grates of the grill. This will create a nonstick grilling surface. Grill the steak for 7 minutes per side for medium-rare. Remove the steak to a cutting board and let it rest for 10 minutes. While the steak rests, grill the mushrooms and onions for about 5 minutes per side so they have a nice char. Brush the cut sides of the ciabatta bread with a little bit of oil and grill for a minute to toast. Slice the mushrooms, separate the onion slices into rings, and slice the steak, paper-thin, against the grain.
Now you are ready to put this awesome sandwich together. To assemble, spread both sides of the bread with the arugula mayonnaise. Lay several slices of flank steak on the bottom bread half and mound with mushrooms and onions. Cover with a couple of slices of fontina cheese and cap it all with the top half of bread. Slice the loaf into 4 sandwiches. Garnish with arugula and serve. It's a beautiful thing.