Step 1

Stir together first 3 ingredients in a large bowl. Combine flour and next 3 ingredients; gradually stir into egg mixture. Set aside.

Step 2

Melt butter in a large skillet over medium heat; add onion, and cook, stirring often, 30 to 40 minutes or until onion is caramel colored. Remove onion from heat.

Step 3

Stir onion into egg mixture; spoon into a lightly greased 13- x 9-inch baking dish.

Step 4

Bake at 350° for 30 minutes or until set.