Casa Dani
Casa Dani is a legendary bar in Mercado de la Paz whose tortilla de patata (potato omelet) is easily the best in town, and perhaps the country (if first place in the National Spanish Omelet Championship of 2019 is any indication). Each hefty wedge is packed with caramelized onions and served hot and slightly runny. Adventurous eaters should opt for the con callos version, topped with spicy tripe. The €13 prix fixe, which hinges on market ingredients, is a great lunch deal if you're not in a rush (prepare for long lines to be seated).