Wash the spinach several times to remove any grit. Drain and pat dry. Bring a saucepan of lightly salted water to the boil. Blanch the spinach for 30 seconds, then drain and refresh under cold running water. Drain well. Place the spinach in a clean tea towel and wring out the excess water. Roll the spinach into a ball, place on a chopping board and thinly slice. Using a fork, lightly beat the eggs with a pinch of salt in a bowl. Set aside. Heat the oil in a 20-centimetre non-stick frying pan over a low heat. Cook the garlic until softened but not browned, then increase the heat to high and add the spinach. Cook for one minute, stirring constantly. Pour the beaten egg into the pan and for the next minute or so, using a flat plastic spatula, fold the egg through the spinach mixture, moving the outer edge of the mixture into the middle of the pan. Reduce the heat to low and cook without stirring for one to two minutes. Remove from the heat, cover with a lid or plate and leave for five minutes to allow the residual heat in the pan to finish cooking the tortilla. Gently slide the tortilla off the pan onto a warmed plate. Sprinkle with a little salt and serve warm.