Add vanilla, cinnamon, nutmeg, and salt to a medium bowl and whisk together until it makes a paste. Add eggs and whisk with paste. Add half and half and whisk together. Set aside.

Slice bananas and add to a separate medium bowl. Add brown sugar and stir together until the brown sugar turns into a paste. Set aside. Place chopped nuts into a shallow bowl or dish and set aside. 

Place 4 slices of bread in a rectangular baking dish in one even layer. Scoop bananas onto slices of bread , about 1/3 cup per slice. Place remaining slice on top of each sandwich. 

Pour custard mixture over the sandwiches. Let them soak for 1 minute and then flip. Let them soak for 1 more minute. 

Remove from custard and place into chopped nuts. Press nuts into the french toast until completely covered. Set aside on baking sheet or large plate. 

Heat 1 1/2 tablespoons of butter in a large saute pan over medium heat. Once butter has melted and begins to bubble, place two sandwiches in pan and cook for 3 minutes. Flip and cook for another 3 minutes on the other side. Repeat with remaining 1 1/2 tablespoons butter and last two sandwiches. 

Slice into triangles and serve immediately. I don't think you need syrup but feel free to serve with the french toast if you just gotta have it. Enjoy!