In the November 1996 issue of Living, we baked mini frittatas in muffin tins. Now we're cutting to the chase (and making post-party cleanup easier) by cooking up a singular masterpiece and slicing it into scrumptious squares.
Preheat oven to 425 degrees. Whisk together milk, flour, and 1 1/4 teaspoons salt. Add eggs; whisk to combine. Stir in spinach, red peppers, and cheese.
Line a 9-by-13-inch baking dish with lightly oiled parchment, leaving a 2-inch overhang on two sides. Pour in egg mixture; bake until just set, 18 to 20 minutes. Let cool 10 to 15 minutes.
Using parchment, transfer frittata to a cutting board. Cut into 1 1/2-inch squares.