Preheat the oven to 350°F. Spritz 10 muffin cups liberally with cooking spray. Set aside
Whisk together the eggs, cream, grated Parmesan cheese, salt, pepper, ground mustard and a dash of nutmeg.
In a medium skillet cook the diced bell peppers, onion and mushrooms in 2 Tbsp of butter until softened and browned. Around 3-5 minutes.
Divide the cooked vegetables between the muffin cups. Sprinkle with ½ of the shredded Colby-Jack cheese.
Fill the muffin cups ⅔ full with the beaten eggs. Sprinkle each with the remaining shredded cheese.
Bake for 18-20 minutes until puffy, golden and set when gently shaken. The eggs will deflate slightly when removing from the oven.