Preheat oven to 350°. Whisk together first 7 ingredients in a large bowl; stir in bread cubes and 1 cup each Gouda and Parmesan cheeses.
Remove and discard root ends and dark green tops of leeks. Cut in half lengthwise, and rinse thoroughly under cold running water to remove grit and sand.
Melt butter in a medium skillet over medium heat. Add leeks, and cook, stirring occasionally, 7 to 8 minutes or until tender. Add garlic, and cook, stirring constantly, 1 minute. Fold leek mixture and bacon into egg mixture. Pour into a lightly greased 11- x 7-inch baking dish. Sprinkle with remaining 1/4 cup each Gouda and Parmesan cheeses.
Bake at 350° for 35 to 40 minutes or until center is set. Let stand 5 minutes.