The frittata was wonderful! Three of use ate it ALL! I used a 9” black iron skillet, and it worked fine. The skillet was marked 10 ½ on the bottom, but the diameter at one-inch depth is 9 inches. Using our old friend Monsieur Pie R. Square, the volume of our skillet is exactly 54% of the 9×13 casserole dish called for in our recipe. So, we cut the recipe in half. From the picture of our finished product, our math was correct and we passed the ACT (Acceptable Culinary Techniques). The three of us ate 127 in3 of voluminous frittata, and it was spectacular!
By the way (BTW), we used 2 lbs. of asparagus trimmed to 1 ½ lbs. The “we” is my step-son, and partner-in-the kitchen, Derek.