Put the butter and flour into a large mixing bowl. With your hands rub the butter into the flour until it resembles breadcrumbs. Next add the ground almonds and icing sugar and continue to rub the mix together.
Add the water and egg, then quickly mix it all together with your hands. Once combined you should be able to shape the dough into a ball. Wrap this ball of dough in cling film and leave in the fridge overnight.
Preheat your oven to 180c (355f). Spread some icing sugar on your work surface to stop the dough sticking. Take your dough from the fridge and roll out. This gluten free dough will be a little 'wetter' and 'sticker' than regular dough so you need to try and roll it out quickly. Line your pie tin with the dough then bake until the crust turns golden, this should take about 20 minutes.
Take the blind baked crust out of the oven, but leave it in your pie tin, and set aside.
Cut the chocolate and butter into small pieces and place in a large heatproof mixing bowl then add the sea salt. Fill a saucepan about 1/4 full with water and simmer over a medium heat. Place the heatproof bowl containing your butter, salt and chocolate on top of the saucepan of simmering water. Once the butter and chocolate are melted stir gently to ensure a smooth consistency.
Set the bowl containing the melted chocolate and butter aside. Using an electric mixer combine the eggs, vanilla and sugar on a medium speed. Slowly pour this egg/sugar mix into your chocolate mix, string constantly until combined.