Preheat oven to 350 degrees and spray square 13x9 pan with non-stick cooking spray. Cube bread and place into prepared pan. Using a whisk, mix together peanut butter, milk, vanilla and cinnamon in a medium sized bowl. It doesn't have to be smooth, I like having small chunks of peanut butter. Pour egg mixture over bread cubes. Top with berries (stopping here you can pop this in the fridge instead and bake in the morning).
Pop into the oven and bake until egg custard is set, about 40 minutes. When is it done? The french toast will pull away from the pan a bit, the top will be browned and the whole thing will puff up a bit. Also, a knife stuck into the center will be pretty clean.