Preheat oven to 350. Line a muffin tin with paper liners or generously grease the muffin pan.
In a mixing bowl, combine all base ingredients and whisk until combined. Using ¼ cup measuring cup, pour egg mixture into prepare pan or cups. Each cup should be about 90% full.
Chop, shred, or dice add-in ingredients. Sprinkle as desired into each egg cup and shake in a little extra salt/pepper. Gently stir each cup to incorporate the add-ins.
Baked for 20 minutes or until toothpick comes out clean and there is no visible liquid egg on top.
Let cool in the muffin cups briefly to finishing setting. Remove from liners or pan after about 10 minutes. Serve warm or let cool completely before storing in the fridge for 5 days or freezing for a few months. Enjoy!