In a large bowl, whisk together the eggs, milk, condensed milk. Add bread cubes, tossing until evenly coated; set aside. Toss with a spoon occasionally to make sure liquid is evenly absorbed.
In a separate bowl, toss peaches with cornstarch, sugar, and lemon juice. Place in a 4-quart baking dish that has been sprayed with nonstick cooking spray. Spread soaked bread cubes evenly over the top.
In another bowl, whisk together the flour, cinnamon and brown sugar. Cut in the butter with a pastry cutter or fork until the mixture resembles small peas; scatter evenly over the top of the casserole.
Bake, uncovered, for 30 to 40 minutes, or until cooked through and bubbly around the edges. Serve topped with whipped cream or ice cream, if desired.