Heat the oil in a large non-stick frying pan, add the potatoes, onion and garlic, if using, cover and fry gently for 15 minutes, stirring from time to time until the potatoes are tender.
Meanwhile, make the sauce. Fry the onion in the oil in a saucepan for 5 minutes until just beginning to brown. Add the garlic, tomatoes and paprika and cook for 2 minutes. Stir in the almonds, season and simmer for 10 minutes until thick.
Beat the eggs, measured water and some seasoning together. Pour into the frying pan with the potatoes and cook for 4–5 minutes without stirring, until the base is golden and the top almost set. Transfer the pan to a hot grill and cook the top of the tortilla for 4–5 minutes until browned and set. Loosen the edges of the tortilla and turn out on to a plate. Leave in a cool place until required.
When ready to serve, cut the tortilla into wedges and arrange on small serving plates with spoonfuls of the sauce and a few olives, if liked.