Preheat the oven to 400 degrees F.
In a large bowl, whisk together the eggs, milk, and sweetened condensed milk. Add the day-old French bread cubes, tossing until evenly coated; set aside.
In a separate bowl, toss the peach chunks with cornstarch, granulated sugar, and lemon juice. Place in a 4-quart baking dish that has been sprayed with nonstick cooking spray.
Spread the soaked bread cubes evenly over the top.
In another bowl, whisk together the flour, ground cinnamon, and brown sugar. Cut in the cold 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.
