In a small saucepan, combine the sugar and water and heat until the sugar dissolves. Remove from heat.
Make the frangipane:
In a medium bowl, cream together the softened butter and sugar until light and fluffy.
Add in the eggs, vanilla, almond extract and stir to combine.
Next, add in the almond flour and use a spatula to incorporate the mixture.
Assemble:
Preheat oven to 350°F. Line a baking sheet with parchment paper.
Slice the croissants in half lengthwise (not cutting it completely through).
Brush the sugar syrup on the insides of each croissant.
Divide the frangipane filling into 4 and place about ¼ of the mixture on one half of the croissant. (Leave about 2 tablespoon of the filling for brushing on the tops).
Place the top back on.
With the remaining frangipane, smear about ½ tablespoon onto the tops of the croissants.
Sprinkle the top with flaked almonds.
Bake in the oven for 25-30 minutes until the filling is baked through. (Place a piece of foil to cover at around 15 minutes if the tops are browning too quickly).