- about 2 tbsp. olive oil, divided
- 1 medium onion, sliced into half rings
- 2 garlic cloves, minced
- 3 Portobello mushroom caps (about 20 oz. total), cleaned and sliced into thin strips
- 1 cup vegetable broth
- 1 tbsp. soy sauce
- 1 tbsp. vegan Worcestershire sauce
- 1/2 tsp. dried thyme
- 1/4 tsp. liquid smoke(optional, but highly recommended)
- 1/4 tsp. black pepper
- 2-6 inch sandwich rolls or baguette sections, sliced open
- horseradish mustard
- Coat the bottom of a large skillet with 1 tablespoon of oil and place over medium-low heat. Add onion and toss a few times to coat with oil. Allow to cook until caramelized, about 20 minutes, flipping occasionally. Add garlic and cook about 2 minutes more. Transfer onions and garlic to a plate.
- Coat skillet with another tablespoon of oil and raise heat to medium. Add mushroom strips. Avoid overcrowding the skillet. A little overlapping is okay, but work in multiple batches if needed (I needed two), adding a bit of oil between batches if needed. Cook until lightly browned, about 5 minutes. Flip and cook 5 minutes more on opposite sides.
- Return onions to skillet and add broth, soy sauce, Worcestershire sauce, thyme, liquid smoke and pepper. Bring to a simmer and allow to cook, stirring occasionally, until liquid is reduced by half, about 5 minutes.
- Slather the insides of rolls with horseradish mustard. Use a slotted spoon to remove onions and mushrooms from skillet, pressing lightly to squeeze out any excess juice. Divide onions and mushrooms into rolls. Top with cheese if you like. Pour cooking liquid into a small bowl and serve with sandwiches, for dipping.