In an oven proof skillet, cook onion in oil until tender. (I like to use my cast iron pan.) Add potatoes and stir until potatoes are slightly browned. Remove from heat.
In a separate bowl, mix together eggs, sour cream, and cheese. Pour over the potato onion mixture.
Bake at 400 for 15-20 minutes or until eggs are done. Cool about 5 minutes and cut into wedges and serve.