Mushroom Onion Melt

This Mushroom Onion Melt is the perfect balance of sweet caramelized onions and deeply savory sautéed mushrooms, layered together for a rich, cozy bite.

This Mushroom Onion Melt layers sweet balsamic-sautéed onions with buttery, golden mushrooms for the ultimate sweet-and-savory combo. The richness of the mushrooms pairs perfectly with the jammy depth of the onions, creating a filling that’s bold but beautifully balanced.

Melted fontina cheese ties everything together with its creamy, slightly nutty flavor, seeping into every nook of the sourdough bread. Toasted until crisp on the outside and perfectly gooey in the center, this sandwich is cozy, indulgent, and packed with flavor in every bite.

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Mushroom Onion Melt

This Mushroom Onion Melt is the perfect balance of sweet onions and deeply savory sautéed mushrooms, layered together for a rich, cozy bite.

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Ingredients

Serves 2 sandwiches

1x2x3x

• ▢ 4 slices sourdough bread
• ▢ 1 medium yellow onion, thinly sliced
• ▢ 8 oz mixed mushrooms I used a mix of shiitake & portobello
• ▢ 1 tbsp balsamic glaze
• ▢ 1 cup shredded fontina cheese
• ▢ 5 tbsp butter
• ▢ 2 sprigs of thyme
• ▢ Salt and freshly cracked black pepper

Instructions 

• Sauté the onions: Using a mandolin or knife, thinly slice the onion. Heat 2 tbsp butter in a skillet over medium heat. Add the sliced onions with a pinch of salt and pepper and cook, stirring occasionally, for 10 minutes until soft and slightly golden. Drizzle in the balsamic glaze and cook another 2–3 minutes until jammy. Remove from the pan and set aside.
• Sauté the mushrooms: In the same skillet, 2 tbsp butter over medium-high heat. Slice mushrooms and add to pan along with sprigs of thyme. Let them cook undisturbed for a few minutes to develop color. Stir and continue cooking until golden and tender, about 6–8 minutes total. Season with salt and pepper.
• Assemble the sandwiches: Butter one side of each slice of sourdough. On the unbuttered side, layer fontina cheese, a generous spoonful of balsamic onions, sautéed mushrooms, and a little more cheese. Top with the second slice of bread, buttered side facing out.
• Grill until melty: Heat a skillet over medium. Cook sandwiches 3–4 minutes per side, pressing gently, until the bread is golden and crisp and the fontina is fully melted.

  Slice and serve warm — crispy on the outside, sweet and savory, and irresistibly gooey in the center.

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