Heat the oven to 200C/180C fan/gas 6. Spread the flaked almonds out over a small baking tray and bake for 6-7 mins until lightly golden. Cut the croissants through the middle using a small, serrated knife so you have two halves. Set aside.

Mix 50g of the caster sugar with 75ml water in a small saucepan. Squeeze in a little lemon juice, then gently melt over a low heat, stirring until the mixture is completely clear. Turn up the heat a little and cook for 2-3 mins more until you have a lightly thickened, viscous syrup. Remove from the heat and set aside.

To make the frangipane, put the butter, remaining 150g sugar, the vanilla, ground almonds, almond extract and lemon zest in a large bowl (or, do this in a stand mixer). Beat using an electric whisk for 4-5 mins until light and fluffy, then crack in the egg and a small pinch of salt. Continue to beat for a few minutes until combined, scraping down the sides of the bowl as you do.

Brush a little of the syrup over the inside of each croissant using a pastry brush. Spoon a few tablespoons of the frangipane over the base of each croissant, then spread roughly 1 tbsp over the top half. Sprinkle a few flaked almonds over the frangipane on the base, along with a few pieces of chocolate, if using. Sandwich the croissant halves together, then put on a baking tray lined with baking parchment. If you like, spread a small amount of frangipane in a thin line down the centre of the top of each croissant, then sprinkle over a few flaked almonds.

Bake for 18-20 mins until the frangipane is bubbling and the almonds are golden brown. Leave to cool for at least 15 mins before eating warm. Best eaten on the day they are made, but will keep in an airtight container for up to two days.