Preheat oven to 425°F. Peel and cut sweet potatoes to 3/4-inch thick pieces. Thinly slice red pepper into strips. Chop broccoli into bite-size pieces (~3/4 inch). Lightly spray an 8x8-inch baking pan with cooking spray and line with parchment paper, leaving some as an overhang for easy removal.
Add veggies onto an extra-large (15x21-inch) sheet pan. (The veggies need to have plenty of room so they’ll roast, not steam.) Add the oil, garlic powder, onion powder, Italian seasoning, plus salt and pepper to taste. (I add 3/4 tsp salt and 1/2 tsp pepper). Toss vegetables well to coat and spread out as much as possible in an even layer. Roast for 20–25 minutes (undisturbed) or until tender and nicely charred. Remove and let slightly cool. Once you remove veggies, reduce oven temp to 350°F.
In a large bowl, whisk together eggs, heavy cream, plus 3/4 teaspoon each of salt and pepper. Briskly whisk until smooth.
Add 2/3 of slightly cooled vegetables into the prepared 8x8 pan. Add Cheddar cheese, then pour the egg mixture over of everything. Add Swiss cheese then remaining vegetables on top in an even layer. Tap the pan on a counter to even everything out. Sprinkle Parmesan evenly over the top.
Bake 37–42 minutes or until the center is set and jiggles only slightly. Remove from oven and let cool for 5–10 minutes before using the paper overhang to lift it out of pan and onto a cutting board to cut and serve.
Video
Notes
Note 1: Grate a block of sharp Cheddar on the large holes, then measure. Pre-grated cheese contains preservatives that keep the shreds from clumping together in the bag, but they also keep the cheese from melting smoothly and will cause a greasy frittata.Note 2: Grated Parmesan (in the can) is very salty and won’t melt as nicely in this recipe. I highly recommend grating a block of Parmesan cheese on the large holes of a grater.Storage: Not serving right away? Transfer to a wire cooling rack and pull out parchment paper from underneath (or it gets soggy). Cut and store in fridge for 3–5 days or freeze leftover pieces (Reheat in microwave).