Potato Tortilla with Tomatoes and Mushrooms
Rinse the potatoes, peel, slice finely with a mandoline, and dry on a paper towel. Peel onion, chop finely. Trim mushrooms and finely chop.
Heat the oil. Fry onions, potatoes, and mushrooms over medium heat for 10 minutes. Season with salt and pepper.
Blanch the tomatoes in boiling water, rinse with cold water, peel, and cut flesh into thin slices. Whisk the eggs and pour over the potatoes. Add the tomato slices and sprinkle cheese on top. Cook on low heat until eggs are set. Using a plate, flip over the tortilla and cook for another 5 minutes.
Remove the tortilla from the pan, and cut in half. To serve, garnish with watercress, chile pepper, parsley, and potato chips.