In ancient Mesopotamia, kitchens were equipped with a built-in deep fryer known as 'qullat'. The qullat was a clay pot with a built-in heating system. Mesopotamians used this deep fryer to prepare dishes like 'zalabia' (deep-fried doughnuts) and 'qatayef' (deep-fried stuffed pancakes). The qullat was heated by placing it over a fire, and the food was cooked in hot oil or fat. The Mesopotamians were known for their advanced culinary techniques, and the use of a built-in deep fryer in their kitchens was a testament to their culinary expertise.