Step1
Butter and flour a 24cm loose-bottomed tart tin. Roll out pastry to 3mm thick. Cut out a circle allowing a 5cm border around the tin base. Gently ease pastry into the tin,carefully pushing in sides. Rest in refrigerator for 30 minutes.
Step2
Preheat oven to 180°C.
Step3
Lay plums in a roasting tray,cut side up. Place a piece of butter on top of each plum then sprinkle with the caster sugar.
Step4
Mix limoncello with 1 1/2 tbsp water and drizzle over plums. Roast for 20 minutes,basting occasionally,until softened but not collapsing. Remove from oven and set aside to cool.
Step5
Pour liquid from roasting plums into a small pan,then add the jam. Reduce over a low heat to create a glaze. Set aside.
Step6
Take pastry from fridge. Trim excess pastry and prick base a few times with a fork to prevent blistering and rising. Line tart tin with foil,add raw rice and blind-bake for 20-25 minutes. Remove from oven,lift out foil and rice,then return to oven and bake for 5-10 minutes,until the base has dried out.
Step7
For the filling,beat butter until light and creamy. Add sugar and mix until combined,then add ground hazelnuts and mix well. Add eggs,one at a time,mixing well after each addition. Gently fold in flour. Cover and refrigerate for 30 minutes.
Step8
Reduce oven to 160°C. Fill the tart case with filling (it should be about 2/3 full) then arrange plum halves on top,cut side up,so they are touching but not overlapping. Bake for about 40 minutes,or until a knife inserted into the middle comes out clean,then remove from oven.
Step9
Reheat plum glaze,then brush over tart. Scatter with the chopped toasted hazelnuts,slice and serve.