Preheat oven to 350 degrees F. Lightly grease 3-quart oven-safe casserole (8 x 10-inch or similar) with 1/2 tablespoon butter. In large bowl, whisk together egg yolks, buttermilk, cream, 1/3 cup syrup, vanilla and salt; reserve.
On ungreased rimmed baking pan, spread waffle pieces in even layer and bake for 12-15 minutes or until crisp and lightly toasted. Increase oven temperature to 375 degrees F.
Add waffle pieces and bacon to buttermilk mixture and toss to coat evenly. Pour into prepared casserole and tightly cover with foil.
Bake for 45-50 minutes and remove foil. Melt remaining butter and brush over top of casserole and bake, uncovered, for another 10-15 minutes or until top is crisp and toasted. Top with fresh berries and remaining maple syrup, dusting with powdered sugar if desired, and serve warm.