Start by making the pastry. Place the flour, ground almonds, icing sugar and salt in a large bowl and mix well.
Add the cold, cubed butter and rub it in using your fingertips until the mixture resembles fine breadcrumbs and no lumps of butter remain.
Add the cold vodka (if using) and mix to combine. Gradually add enough cold water to bring the pastry together into a ball. Shape the pastry into a disc (don't knead it), wrap and refrigerate for about an hour until firm enough to roll out.
Roll the pastry out on a lightly floured surface into a circle big enough to line a 25cm round tart tin. Press the pastry right into the corners then roll over the top of the tin with a rolling pin to trim off the excess.
Prick the base of the pastry shell all over with a fork then place it in the freezer for 20 minutes until solid. Meanwhile preheat the oven to 180°C/160°C fan/350°F/gas mark 4.
Line the pastry case with baking parchment or tin foil, pressing it right into the corners, then fill with baking beans or dried rice, making sure that the sides are propped up.
Bake for 20 minutes then remove the tin foil and baking beans and return the tart shell to the oven for a further 10 minutes until very pale golden. Remove from the oven and set aside.
To make the frangipane, whisk together the ground almonds, plain flour, cornflour, baking powder and sugar. Add the milk, melted butter and almond extract and whisk until smooth.
Spread a layer of apricot jam over the base of the pastry case then spread or pipe the frangipane over the top.
Drain the apricots really well and pat them dry with kitchen paper.
Arrange the apricot halves on top of the frangipane and scatter over a handful of flaked almonds.
Bake the tart for 1 hour, until the frangipane is set and a skewer inserted into the centre comes out clean.
Allow the tart to cool in the tin for about half an hour then carefully turn it out onto a wire rack.
To make the glaze, place the apricot jam and the water in a small pan and heat until melted. Press the jam through a fine mesh sieve so that it is smooth.
Gently brush the top of the tart with the jam. You can add a drop more water if it is too thick to brush. Allow the tart to cool before serving.