Preheat the oven to 160'C.
Use a sharp knife to scrape the seeds from the vanilla pod and add them to egg whites.
Whisk the egg whites with 150g caster sugar. Whisk until you have a stiff and glossy meringue mixture.
Place the icing sugar and the almond powder in a blender. Blitz and then sieve this mixture into a bowl to ensure that you have a very fine, lump-free powder.
Incorporate the dry ingredients into the meringue mixture. Use a spatula to cut and fold the mixture until is smooth, shiny and ribbon-like.
Fill a piping bag with the macaroon mix and pipe the macaroons onto a lined baking tray.
Leave the macaroons to dry slightly for 15 minutes at room temperature and then bake in the preheated oven for 10-15 minutes.
Bring the milk to the boil.
Whisk the egg yolks with 50g of caster sugar and the flour. Pour on the boiling milk.
Return to the pan and cook for a further 3 minutes until the mixture thickens significantly.
Pour this mixture on to a large tray lined with cling film and place in the fridge to cool.
To finish the filling: Place the cold creme patissiere in a food processor and beat in the praline paste and the butter.
Assemble the macaroons, using the praline cream to stick them together.
«For a gluten free filling, replace the plain flour with 30g of cornflour. To cool the filling for your macaroons more quickly, place the filling in a bowl and cool down whilst stirring over a bowl of ice.»