Mix warm water, sugar, vanilla extract, and hazelnut syrup. Stir until dissolved.
Prepare the filling. Mix the almond flour/meal, eggs, butter, sugar.
Cut each croissant in half horizontally with a serrated knife.
Dip each croissant into the syrup mixture.
Add 2 tbsp of the filling inside of the croissant and 1 tbsp on top of the croissant.
Add sliced almonds on top.
Place the filled croissants on a baking sheet lined with parchment paper. Bake at 350°F for 20 minutes or until golden.
Dust with powdered sugar on top.
Let the croissants cool for a few minutes, then dust with powdered sugar. Serve warm and enjoy!
Notes
*If you want to get really fancy, you can drizzle some melted chocolate on top of the powdered sugar for a decadent finishing touch.**You can experiment with different flavors by adding spices like cinnamon or nutmeg to the almond filling, or try swapping out the hazelnut syrup for another flavor like orange or raspberry.