Begin by preparing the almond filling. In a mixing bowl, combine the unsalted butter, granulated sugar, almond meal, 2 large eggs, and either vanilla or almond extract. Mix until well combined and set aside.
3/4 cup unsalted butter, 3/4 cup granulated sugar, 1 1/2 cups almond meal, 2 large eggs, 1 1/2 teaspoons vanilla or almond extract
Slice the croissants in half from top to bottom.
6 large croissants
Spread the prepared almond filling generously on the sliced sides of the croissants.
Place the filled croissants, filling side up, into a buttered baking dish.
Sprinkle sliced almonds over the top of the filled croissants.
8 Tablespoons sliced almonds
In a separate bowl, whisk together the custard ingredients: 1 cup milk, 3 eggs, 1/4 cup sugar, and 1 tsp salt until well combined.
1 cup milk, 3 large eggs, 1/4 cup sugar, 1 teaspoon salt
Pour the custard mixture evenly over the filled croissants in the baking dish. Make sure all the croissants are soaked in the custard.
Cover the baking dish with aluminum foil.
Preheat the oven to 375 degrees Fahrenheit (190 degrees Celsius).
Bake the covered croissant French toast in the preheated oven for approximately 20-25 minutes.
Remove the foil, and continue baking for an additional 5-10 minutes or until the top is golden brown and the custard is set. Keep an eye on it to prevent over-browning.
Once done, remove the croissant French toast from the oven, and let it cool for a few minutes.
Serve warm, topped with additional sliced almonds or powdered sugar, if desired.