First make the sugar water coating. Boil the water with the sugar and vanilla extract for 3-5 mins, stirring a few times, until the sugar has dissolved. Turn off the heat, pour into a shallow bowl and let it cool slightly.
Preheat the oven to 175C/350F.
Now make the almond paste/frangipane. Place the ground almonds, butter, sugar
and salt in a bowl and beat with a wooden spoon until fully combined. Add the egg and almond extract and beat again until you get a thick paste. Put to one side.
Place the raspberry jam and cornflour in a small bowl and mix to combine. Carefully fold through the raspberries until coated (the cornflour helps to absorb some of the moisture from the raspberries as they cook, so it's a thick sauce rather than runny raspberry juice that would make the croissants soggy).
Take 4 large croissants and brush them all over with the sugar water, so they're well coated.
Place the croissants on a baking tray and make a horizontal cut in the middle of each one
using a sharp knife. Spoon half of the almond paste inside the croissants. Spoon the raspberry mixture inside, on top of the almond paste - you should have 5 raspberries for each croissant.
Spread the remaining frangipane on top of the croissants and sprinkle on the flaked almonds.
Place in the oven and cook for 12-15 minutes until the almond paste on top of the croissants is golden brown.
Take out of the oven and sprinkle with confectioners' sugar before serving.
*Note - there is egg in this mixture, which, when stuffed into the croissant is warmed but not fully cooked. So if this is being made for anyone who should not be eating raw eggs, I'd leave the almond paste out of the centre of the croissant, and just top the croissant with it (as the top bit will be fully cooked)..Nutritional Information is per serving.