STEP 1 - Peel and slice the onions, Once sliced, saute the onions until tender and translucent in colour. Set aside.
STEP 2 - Clean and peel the potatoes. Using a mandolin, make 1-1.5cm thick slices of potatoes. In a non stick pan, shallow fry the sliced potatoes for about 10 minutes in medium-low heat. Once finished, strain the potatoes. Keep the used oil for future use. Set the potatoes aside to cool.
STEP 3 - In a large mixing bowl, beat 8 eggs together. Add the onions and potatoes. Season with salt. Sit for at least 15 minutes.
STEP 4 - Using a serrated/bread knife, slice the bread into 1 inch bias cuts. Arrange in a baking sheet, drizzle some olive oil over both sides and toast in the oven for 5 to 10 minutes at 250degF, flipping each side thoroughly. You may also do this in a regular toaster over.
STEP 5 - In the same pan used for frying the potatoes, with very little oil, turn the heat up to medium-low. Add the egg mixture and cook for 6-8 minutes per side. When the under portion is lightly browned already, get a plate, slide off the tortilla with the cooked part side down on the plate. Transfer back to the pan and flip quickly. Some of the egg might fall off, but that is fine. Check occasionally if it is cooked and of the same colour as the first side. Be careful not to overcook this because doing so will result to a rubbery tortilla.
STEP 6 - Transfer to a serving plate, and cut into 6 to 8 slices. Serve on top of toasted bread. Garnish with chopped spring onions and dust with pimentón dulce powder. Enjoy!