Mushroom Patty Melt

Instructions

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1. 1 Preheat the oven to 400°F. Gather and prepare all ingredients.
2. 2 In a medium skillet over medium heat, warm ¼ cup vegetable oil. Add the sliced onions and cook, stirring occasionally, for about 45 minutes until caramelized and golden. Remove and set aside, then wipe out the pan for the sandwiches.
3. 3 While the onions are cooking, remove the stems and gills from the mushrooms and place them, cap side down, on a parchment-lined sheet tray.
4. 4 In a small bowl, whisk together the garlic, balsamic vinegar, remaining ¼ cup vegetable oil, soy sauce, and thyme. Carefully pour on the mushroom caps. It's ok if it overflows. Roast the mushrooms in the oven for 20 minutes, then set aside. Once cooled, slice the mushrooms.
5. 5 To assemble the patty melts, lay out the rye bread and spread mayo evenly over all 8 slices. Top each with Swiss cheese and caramelized onions. Add the sliced portobello mushrooms to 4 slices of bread and sprinkle with salt, then close with the remaining 4 slices to form sandwiches.
6. 6 To cook the patty melts, melt 1 Tbsp butter in the skillet over medium heat. Place two sandwiches in the skillet. Toast for 3–4 minutes, then add another Tbsp of butter, carefully flip, and cook for 3-4 more minutes. Repeat with the remaining two sandwiches and butter. Serve and enjoy!