From my knowledge, all of the food is cooked by each vendor on a daily basis. Everything is incredibly fresh, and the vendors take great pride in their preparation. They are a master of their craft and quality is their main focus. Some vendors even cook your food to order! It just depends on the particular item you choose to order for yourself.
The food is usually locally sourced. However, there were vendors selling food with global influences. I saw Japanese dumplings, Indian curries, Mediterranean kabobs and other ethnic inspirations along with traditional Spanish fares. The international influence is a reflection of the diverse population in Madrid and the rest of Spain. There are people of all cultures and origins here. Everyone is sharing a piece of their culture through food!
