In a large bowl, use your fingertips to rub the butter into the flour until it resembles large breadcrumbs. Stir in the egg yolk and a tablespoon of water until a firm dough forms. Form into a ball, wrap with cling film and chill in the fridge for 30 minutes.
Roll the dough out to 1/2 cm thickness and press down into a loose bottomed 23cm/ 2.5 cm deep tart tin. Trim the edges and prick the base all over with a fork. Chill for 20 minutes.
Preheat the oven to 190°C/fan 170°C. Line the pastry with foil and fill with baking beans. Blind bake for 15 minutes. Remove the foil and beans and bake for a further 5 minutes.
Meanwhile, to make the frangipane, use an electric hand whisk to cream the butter and sugar for 2 minutes. Whisk in the eggs until well combined. Then stir in the ground almonds, almond extract and 1/2 tsp of cinnamon.
Core the apples, then slice into 4mm slices, leaving the skin on. Add to a bowl and coat in a teaspoon of the cinnamon and all the nutmeg.
Fill the baked pastry with the frangipane mixture. Place the apples in a concentric ring pattern working from the outside in. Scatter over the flaked almonds. Bake in the oven for 40-45 minutes.
Remove from the oven and leave to cool in the tin for 15 minutes. Carefully remove the tart from the tin and transfer to a serving plate. Sift over the icing sugar and serve warm with vanilla ice cream.