Frittatas can be baked ahead of time. Cool, then refrigerate up to 4 hours. When ready to serve, cover loosely with foil then reheat in a 350ºF oven 5 to 10 min. or just until warmed.
How to Prevent Baked Frittatas from Sticking to Pan
Spray muffin cups well with cooking spray to help prevent the baked frittatas from sticking to the cups. If the frittatas do stick to the cups, use tip of sharp knife to run around edges of frittatas to help release them from the cups.
If there are any empty mini muffin cups in the pan, fill each empty cup with 1 Tbsp. water so the frittatas will bake more evenly.