1. To make the pate sablee:
Rub butter and flour together until a nice golden sandy texture emerges. Let chill for 15 minutes.
2. Add icing sugar and mix, add eggs and knead thoroughly with your hands until it comes together in a smooth ball. Cut into half. Flatten each half lightly into round discs and wrap in cling film and let sit for 10 minutes. You will only need one portion of dough, so freeze the other one for another time, making sure it's well wrapped.
3. Preheat oven to 185C/Gas 4..
4. On a lightly floured surface, roll out one disc until it reaches 3/8 inch thickness. Place inside the pie plate, and roll in edges. Let chill for 10 minutes.
5. Line the pie plate with greaseproof paper and place baking beans on top. Blind bake for 20-25 minutes until dry and a light golden colour.
6. To make the frangipane, using a stand mixer with a paddle attachment, cream the butter and sugar together until light and fluffy.
7. Gradually beat in eggs one at a time, until thoroughly combined.
8. Mix cornflour and ground almonds in a separate bowl. Fold into mixture.
9. Preheat oven to 180 degrees C/170 fan assisted.
10. Fill tart with frangipane.
11. Slice halved plums vertically and lay onto the tart.
12. Bake for 20-30 minutes until filling is set and golden brown.
13. Remove from oven, and let cool.
14. Glaze with apricot jam and sprinkle with toasted flaked hazelnuts.