For which type of egg is a long cooking time on one side essential to avoid a runny yolk?

The type of egg that requires a long cooking time on one side to ensure the yolk is fully cooked is the one referred to as "over well." Cooking an egg over well means that it is cooked until the yolk is completely set and no longer runny. This method typically involves allowing the egg to stay in the pan longer than other preparations, which is crucial to achieve the desired firmness of the yolk.

In contrast, other cooking methods such as over easy, scrambled, and basted allow for variations in yolk texture. For example, over easy eggs are flipped after a short cooking time, resulting in a partially runny yolk, while scrambled eggs are stirred and cooked quickly, ensuring a soft and creamy texture. Basted eggs involve adding water or oil to the pan and covering it briefly, which also results in a runny yolk by not allowing for extensive cooking on one side. Hence, a long cooking time is distinctively essential for eggs cooked over well to achieve a fully set yolk.