I wouldnt do actual french toast in the fermentor. The fats will create a layer at the top of the beer that may mess with the yeast floating to the top. I have a breakfast stout inspired beer that I've brewed a few variations on. The last one I found artificially flavored french toast coffee beans. They smelled amazing, so I figured I'd give it a shot. I used whole beans in the fermentor along with my cacao and vanilla additions. I gotta let it age for another month or so and try it alongside my others I've saved.
Flapjack Breakfast Stout (Chocolate-Coffee-Oatmeal-Maple Imperial Stout)
Flapjack Breakfast Stout (Chocolate-Coffee-Oatmeal-Maple Imperial Stout)