1. First make the shortcrust pastry, it can be made a day ahead and kept in the fridge. Stir together the flour, sugar, baking powder and zest. Add the diced butter and process or rub in until it resembles coarse breadcrumbs.
2. Mix the egg, yolk, vanilla and cream in a separate bowl, pour into the flour mix and stir together just until combined. Give it a quick knead to shape into a ball, wrap in cling film and chill at least an hour.
3. When ready to bake, preheat the oven to 180C/350F/gas 4. Beat the wrapped pastry with a rolling pin to soften, then roll it out and press into the bottom and 1½ cm /1 inch up the sides of a round tart tin or dish, 23cm (9in). You may well not use up all the pastry – the base should be about 1cm (½in) thick. Prick it all over with a fork. Any leftover pastry will make great shortbread fingers.
4. Bake the base loosely covered with parchment and weighed down with baking beans/coins for 15 minutes, remove the weights and parchment and bake it for another 5 minutes. Remove from the oven and cool completely.
5. To make the frangipane, beat the sugar with the butter until fluffy. Beat in the eggs, one by one. Beat in the flour to eliminate the curdling. Fold in the ground almonds.
6. Spoon the frangipane cream into cooled base and spread evenly, including the edges. Place the apricot quarters over the cream, skin side down. Sprinkle lightly with the cinnamon. If using the pistachios, crumble them around the edge.
7. Bake in the oven preheated to 190C/375F/gas 5 for about 30-35 minutes until the frangipane is golden and almost set. Cool in in the tin completely. Any tart left over will keep in the fridge for another couple of days.