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Grilled Portobello Sandwich with Walla Walla Onion Relish

Grilled Portobello Sandwich with Walla Walla Onion Relish

YIELD: 24 servings

Walla Walla Onion Relish:
4 lbs. Walla Walla or other sweet onions, sliced ¼" thick
¼ cup olive oil, divided
1 qt. seeded, diced tomato
½ cup (3 oz.) shredded fresh basil
⅓ cup (3 oz.) seeded, diced jalapeño pepper
¼ cup white wine vinegar
1 tsp. salt
1 tsp. pepper
Grilled Portobello Sandwiches:
24 (4 to 5 oz. each) portobello mushroom caps
Olive oil, as needed
48 slices sourdough bread
Salt and pepper, as needed
24 (1 oz. each) slices fontina, jack or other mild semi-soft cheese
24 fresh basil sprigs
  1. For onion relish: Divide onion slices between 2 sheet pans. Drizzle 2 Tbsps. olive oil over each pan and toss onion slices to coat. Bake at 400°F, stirring occasionally, until tender and lightly browned, about 30 minutes. Remove from oven and let cool.

  2. Coarsely chop onion. Mix onion with remaining relish ingredients. Let stand at room temperature for about 30 minutes to marry flavors.

  3. Per order: Lightly score top of 1 portabella mushroom cap in a diamond pattern. On the gill side, cut a shallow X in the center where stem was attached. Brush mushroom cap with olive oil and season with salt and pepper. Bake at 550°F until tender and lightly browned, turning once, about 5 minutes.

  4. Meanwhile, grill or toast 2 slices of sourdough.

  5. To assemble sandwich: Place 1 portobello cap on 1 slice grilled bread. Top with ⅓ cup relish and 1 slice cheese. Partially cover with second slice of bread. Broil in oven or salamander until cheese melts, about 1 minute. Garnish with a basil sprig.
    Recipe and photo: Sodexo Corporate Services' “4 Seasons of Flavor” promotional series

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