6 Tbsp. extra-virgin olive oil, preferable Spanish, plus more for brushing
½ small red onion, thinly sliced
Salt and Pepper
¾ pound Cremini mushrooms, cut into ½ inch pieces
¼ cup coarsely chopped flat-leaf parsley, plus more for garnish
8 large eggs
In a 10-inch nonstick skillet, heat the 6 tablespoons of olive oil. Add the onion and a generous pinch of salt and pepper. Cook over moderate heat, stirring occasionally, until softened, about 5 minutes. Add the mushrooms and season with salt and pepper. Cook over moderately high heat, stirring occasionally, until the mushrooms are tender and golden, about 7 minutes. Stir in the 1/4 cup of parsley.
In a large bowl, beat the eggs with a generous pinch of salt and pepper. Pour the eggs into the skillet and cook over moderate heat, gently stirring and lifting the tortilla, until the edge is set and the center is still loose, about 7 minutes. Put a large, flat plate on top of the skillet and carefully invert the tortilla onto the plate. Slide the tortilla back into the skillet and cook until the center is set, 1 to 2 minutes longer. Slide onto a serving plate, brush with olive oil and garnish with parsley. Serve right away.
The tortilla can be kept at room temperature for up to 3 hours.