Place the glaze ingredients into a small pan and bringing to the boil. Bubble for a minute or two until the sugar dissolves, then turn off the heat and allow to cool slightly.
Frangipane
Now make the frangipane. Place the ground almonds, butter and sugar in a bowl and beat together with a wooden spoon.
Add in the salt, egg and almond extract and mix until combined.
Croissants
Cut each croissant lengthways, not all the way through, but leave it joined at the back edge
Place the croissants on a baking tray. Depending on the size of the croissants, put a tablespoon or 2 in each croissant and spread evenly.
Brush the glaze liberally over the croissants
Sprinkle the flaked almonds on top and place the croissants in the oven for 10 minutes. The top should be golden and the almonds are getting crispy brown
Take out of the oven. Allow to cool for few minutes. Sprinkle icing sugar on each of the croissants and serve,
Notes
The leftover Frangipane will keep for a week in the fridge.