Preheat oven to 335 degrees F. Grease ceramic or glass pie plate. Melt butter in small sauce pan, add onion and saute until translucent.
While onion is cooking, beat eggs into a medium-size bowl. Stir in cottage cheese and shredded cheese.
Defrost spinach in microwave (or defrost in fridge day before). Turn off heat under onions. Squeeze out liquid (with potato ricer, potato masher or by hand). Add spinach to onions in pan. Mix well with fork.
Add spinach mixture to egg mixture and stir well. Pour batter into pie pan.
Bake for 45 minutes. Slice into six pieces. Can be served at room temperature. Note: Can make dish night before and bake (or reheat) in morning.