Make a slit, lengthways, in each of the croissants - so you're forming a pocket in the 'belly' of the croissant. Put to one side.
Make the glaze first, by placing 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.
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.
Carefully dip (but don't soak!) each of the croissants in the glaze (all over) and allow the excess to drip off. It will be very watery, but don't worry, this glaze is just there to add a little moisture to the croissants and to make the outside a little crispier when cooked.
Place the croissants on a baking tray. Take a spoon and spoon half of the frangipane mixture inside the croissants. Use the spoon to spread it all over the inside of the croissants.
Spread the rest of the frangipane on top of the croissants. Sprinkle the flaked almonds on top and place the croissants in the oven for 10-12 minutes - until the top is golden brown and crisp (the inside should be hot, but it won't crisp up - it will be like a creamy paste).
Take out of the oven and leave to cool slightly, then spoon the Nutella inside and arrange the sliced strawberries inside. Serve immediately.