Apple, leek, and gruyere frittata

This was a lighter version, using 4 egg whites and 4 whole eggs. We generally followed this recipe but made ingredient and method modifications: http://www.geniuskitchen.com/recipe/apple-and-leek-frittata-114432 First, we preheated the oven to 425. Second, we used a large (9-10”) cast iron pan. Third, we added ¾ cup shredded gruyere cheese at two steps: (1) we sprinkled 1/3 of the shredded gruyere over the apple-leek mixture just prior to pouring the egg mixture overtop; and (2) after pouring the egg mixture in, we topped it with the remaining 2/3 of the gruyere. Fourth, at this stage, we let the frittata cook on low heat until the egg mixture slightly set. At that point, we placed the pan in the 425 degree oven and baked until the frittata finished cooking (about 12-14 mins). Finally, at the end of cooking, we placed the frittata under the broiler (set on Low) to brown the top (about 1 min). We served this with some lightly dressed tomatoes. (Apr. 2018) Note: We used a honeycrisp apple after learning that it pairs well with Gruyere. Also, perhaps due to the fresh sage, this frittata tastes like it contains sausage when it actually is vegetarian.Variation: We converted this recipe into mini-frittatas as follows: first, we oiled a cupcake tin (12-muffin size) and preheated the oven to 425. Second, we sauteed the leeks, apple, and sage in a saute pan, and then let cool slightly. Separately, we made the egg mixture and added most of the shredded gruyere (setting aside about 2 Tbsp for topping). When the leek-apple mixture had cooled a bit, we stirred it into the egg mixture. Third, we evenly divided the raw frittata mixture among the cupcake tins (about 2/3 full), then topped each filled cupcake tin with the remaining shredded gruyere. We baked at 425 for about 20 mins, and then turned on the broiler to high and browned the tops (about 2 mins). (Jan. 2020)