Peel potatoes and chop onion and garlic. Slice potatoes like thick potato chips. Fry in a 9-inch skillet in medium-hot oil. Add the onions and garlic. Cook slowly, about 10 to 15 minutes. Potatoes should be tender, not brown. In a bowl, beat eggs. Add salt and the potato mixture. Stir. Clean or wipe the skillet. Add 4 to 5 tablespoons oil to skillet and heat. Pour the omelette mixture into the skillet. Cook over low heat until set (less than 10 minutes), occasionally using a spatula along skillet rim or shaking gently to loosen sides and bottom. Cover skillet with a large plate or cookie sheet. Hold tightly and flip so that the omelette ends up inverted with the brown side up on the plate or cookie sheet. Add another tablespoon of oil to the skillet and heat. Slide the omelette back into the skillet to brown the underside, 2 to 3 minutes. Serve hot or at room temperature.