This has been a staple recipe for me for quite some time. It's easy and has so many variations you can choose! My guests love it.
I use 5 x 5 individual ramekins. Spray each ramekin with non-stick spray. Place 1/2 cup of hashbrowns in each. Then add one tomato slice and basil (fresh pieces if possible or, off season, dry). Add 1/2 cup cheese.
Mix in large bowl the eggs, sour cream, and mustard. Put a cup of egg mixture in each ramekin. Keep using the egg mixture until it is gone. You should have none left and full ramekins.
Put in a heated 350 degree oven for 45 minutes. It will bubble up. Just before serving put some balsamic glaze on top (available in your local store.). Serve hot.