Open Face Portabella Recipe

Prepare and cook onions

Heat a 10" skillet over medium-low heat. Add 1 tablespoon olive oil and 1 tablespoon butter. Add the thinly sliced onion and a pinch of salt; stir to coat. Cook slowly, stirring every 3–5 minutes, until onions are soft and golden brown, about 20–25 minutes. If they start to stick, add 1–2 tablespoons water. Stir in 1 teaspoon brown sugar and 1 teaspoon balsamic vinegar in the last 2 minutes to help caramelize and deepen flavor. Remove from heat and set aside.

In a small bowl, combine 1 tablespoon mayonnaise, 1 minced garlic clove, 1 teaspoon lemon juice, 1 teaspoon olive oil, 1/4 teaspoon salt and 1/8 teaspoon black pepper. Whisk until smooth and refrigerate until ready to use. Taste and adjust acidity or seasoning as needed.

Prepare mushrooms

Preheat oven to 425°F (220°C). Clean the portabella caps by wiping with a damp paper towel and remove stems. Using a spoon, gently scrape out the dark gills if desired (optional). Pat dry. Brush each cap with 1 tablespoon olive oil (total 2 tbs) and season both sides lightly with 1 teaspoon salt and 1 teaspoon black pepper, dividing evenly between the two caps.

Assemble and bake mushrooms

Place the prepared mushroom caps gill-side up on a rimmed baking sheet lined with parchment. Slice the 2 roma tomatoes into 1/4" rounds and arrange on top of each mushroom cap. Divide the caramelized onions evenly between the two caps, piling some on top of the tomato slices. Crumble 1.5 oz gorgonzola over each cap (total 3 oz). Bake in the preheated oven until the mushrooms are tender and cheese is melted and slightly golden, about 12–16 minutes. Remove from oven and let rest 2 minutes.

Wilt spinach

While mushrooms bake or immediately after removing them, heat a small skillet over medium heat (no additional fat required if pan is nonstick; otherwise add 1 teaspoon olive oil). Add the packed 1 cup baby spinach and sauté just until wilted, 1–2 minutes. Season lightly with a pinch of salt and transfer to a bowl. Keep warm.

While mushrooms cook, prepare the focaccia: brush both sides of each focaccia slice with 1/2 tablespoon olive oil (total 1 tbs). Toast on a baking sheet in the oven for the last 4–6 minutes of the mushroom baking time or in a skillet over medium heat until lightly crisp and warmed through. Remove from oven or pan, and rub the cut side with the halved garlic clove for a subtle garlic flavor.

Place each toasted focaccia slice on a plate. Spread about 1/2 tablespoon of the house aioli on each slice (total 1 tbs divided). Top each with a wilted handful of spinach, then place a baked portabella cap on top, tomato/onion/cheese side up. Spoon any remaining caramelized onion from the baking sheet over the mushrooms. Drizzle a little extra virgin olive oil if desired and finish with a small pinch of flaky salt and a grind of black pepper.

Serve immediately while warm, open-faced. Provide a knife and fork for easier eating.