What type of flour is commonly used to achieve high egg content in popovers?

The correct choice is bread flour, as it has a higher protein content than the other types of flour listed. The protein in bread flour contributes to the development of gluten, which is essential for creating the structure needed in popovers. This structure allows the steam generated during baking to expand and create those characteristic lofty puffs. The increased gluten strength provided by bread flour helps to trap the air and steam, ultimately resulting in a light and airy texture that is desired in a well-made popover.

While all-purpose flour can also be used for making popovers, it may not achieve the same lift and structural integrity as bread flour due to its lower protein content. Cake flour, with its even lower protein content, is suited for tender baked goods but lacks the necessary gluten strength for popovers. Self-rising flour contains baking powder and salt, which can alter the recipe's balance and may not give the desired texture. Thus, bread flour is the best option for creating high egg content and achieving the perfect popover.