First, start by slicing you brioche loaf into 1 inch slices. I used an entire loaf of brioche bread which should render approximately 24 slices.
Next, in a medium bowl, add milk, bailey’s Irish cream liquor, eggs, brown sugar, white granulated sugar and ground cinnamon.
Whisk all the ingredients together making sure to incorporate the eggs well into the mixture.
Prepare a 9×13 baking dish by spraying it with non stick baking spray.
Preheat the oven to 350 degrees F.
Use tongs to dip each slice of brioche bread into the milk mixture. Then transfer the bread to a 9×13 baking dish.
Once you've finished dipping each brioche slice into your milk mixture and transferring them to the baking dish, top them off with any remaining milk mixture. When transferring to the baking dish, place them in a slanted upright position then place the next slice in front of it creating a row of bread slices.
Cover your french toast casserole and refrigerate for 30 minutes or overnight.
Next, bake covered in a preheated 350 degree F oven for 35 minutes.
Cut thin slices of butter and set aside for now.
Uncover and add the slices of butter to the top of the french toast slices and bake for another 10-15 minutes or until golden brown.
Finally, serve topped off with fresh berries and maple syrup or whatever toppings you prefer!