In a small pan, combine the onions and butter and sauté until the onions are soft (don't brown).
In a large bowl, slightly beat the eggs. Add all the ingredients together, including the onions and crackers and stir until blended.
Pour into greased 9" x 13" baking pan.
Cover with plastic wrap and store in the refrigerator overnight.
Remove plastic wrap cover. Bake at 350°F for 45 minutes or until knife blade comes out clean from center. Serve hot.