3 - 3 1/2 pounds of summer squash or zucchini or mixture of both ! -- NOTE: preferably the smaller less seedy ones. It is better to get several small squashes than one or two large ones since the seeds do not take to the boiling well. -- !
2 medium onions
3 large eggs slightly beaten
1 cup mayonnaise
2/3 cup sour cream
2 TB heavy cream [not absolutely necessary but smooths it out]
1 cup shredded parmesan
1 cup shredded white cheddar or Monterey jack or cheese of your choice
2 tb butter
1/4 to 1/2 tsp garlic powder and onion powder, this is really up to your taste
1 TB kosher salt plus salt and pepper to taste
Preheat the oven to 350 degrees F.
Dice onions into large bite size pieces.
Slice squash into 1/2 inch thick slices.
Place squash and onion in a large saucepan, and cover with water. Add 1 tablespoon salt, and bring to a boil. Reduce heat, and simmer until tender, about 10 minutes. Be careful not to let the squash over boil as it will start to disintegrate. Remember, it is also going to cook in the oven. Drain well.
In separate bowl combine 2/3 cup parmesan cheese, eggs, cream, sour cream, mayonnaise, butter, shredded cheddar cheese, and seasonings. Stir to combine. Add well drained squash and onions, mix gently and pour into a 2-quart shallow baking dish.
Spread remaining 1/3 cup shredded parmesan cheese over top. Cover, and bake until set, about 30 - 45 minutes. Uncover, and continue baking until top is browned, about 10 minutes more.