Preheat your oven to 300 degrees F. Arrange the brioche slices on a baking sheet in a single layer and bake for 5 minutes or until slightly dried out. This step helps the bread soak up the custard better.
Spread sliced almonds in a single layer on a separate baking sheet and bake for 3 to 5 minutes until toasty. This adds a lovely crunch and enhances the flavor.
In a microwave-safe bowl, combine almond paste and butter. Microwave in short bursts until softened, then mix until smooth. Stir in a pinch of salt and one lightly beaten egg.
Heat a large non-stick skillet over medium-high heat. Spread ¼ of the almond paste mixture onto four slices of the toasted brioche, then top with another slice to form a sandwich.
In a shallow baking dish, whisk together remaining eggs and whole milk. Dip each sandwich into this mixture, allowing one side to soak for 5 to 10 seconds before flipping.
Coat the skillet with a thin layer of butter. Place the soaked sandwiches in the skillet, cooking for about 2 to 3 minutes on each side until golden brown.
Once golden, transfer cooked sandwiches to a baking sheet while you repeat with the remaining slices.
Place the baking sheet in the oven for an additional 5 to 10 minutes to heat through.
To serve, transfer to plates, sprinkle with toasted almonds, dust with powdered sugar, and drizzle with maple syrup if desired.