Put flour in a medium to large bowl. Add the chilled butter and with the tips of your fingers rub the butter into the flour, till it resembles coarse sand (you don’t want the butter to be totally melted).
Add the egg(s) and bring the dough together to form a ball (you can add a splash of cold water if it’s still too dry, I didn’t need to add any water). Don’t knead the dough too much; you don’t want the pastry to be tough.
With as little handling and kneading as possible. Flatten the pastry into a disk; wrap in cling film and stick it in the fridge to chill for 30 minutes (more if the dough has not firmed up).
To check if the dough is ready, press it lightly with your fingertips, it should leave an imprint but shouldn’t sink into the dough easily.
Very lightly grease an 8 inch tart tin (with a removable bottom). You could use smaller tart tins or rectangular/square ones.
Take the pastry out of the fridge and on a lightly floured surface knead it just a little to bring it together.
Roll out the dough on a lightly floured surface roughly 3 mm thickness. Carefully lift the rolled out pastry and gently press it into the bottom and up the sides of the tart tin.
Trim the edges and patch any cracks with the remaining dough. Place the crust in the fridge to chill for 20 minutes.
Preheat the oven to 200C. Using a fork prick all over the bottom of the crust, then place baking paper on top of the crust
fill it with baking weights or beans or rice (to prevent the crust from rising). Bake in the oven for 15 minutes, after that remove the baking paper and the baking weights.
Put the crust back in the oven for another 5 minutes or until it is a light golden brown colour. Cool the tart shell completely before filling.
If using berries or other fresh fruit for the topping, skip this step. If using rhubarb, cut it into pieces such that fits your tart tin and is roughly the same size in width.
In a saucepan/frying pan add the sugar, lemon juice, vanilla bean (without the seeds) and water. Heat on a med-low flame till the sugar dissolves, then add the rhubarb and simmer for five minutes.
Remove from the heat and let cool, you can leave the rhubarb in the liquid overnight too. Once cool, remove rhubarb pieces from the liquid and put the liquid back on heat to reduce till it becomes syrupy and slightly sticky.
Cut the butter into pieces and put it in a heatproof bowl, place a strainer over the bowl and keep aside.
Whisk together the cornflour, egg yolks and sugar in a bowl. Keep aside
In a saucepan add milk and vanilla seeds and heat it to just below a simmer. Take it off the heat and slowly add the milk to the egg mixture, whisking constantly.
Pour everything back into the saucepan and put it on low heat until quite thick and glossy (about 2-3 minutes). Make sure you whisk it constantly (you can also alternate between a spatula to make sure it’s not sticking in the corner.
Immediately press it through the strainer (in the bowl and strainer kept ready earlier). Mix it in with the butter and cover with plastic wrap, making sure the plastic wrap is directly over the surface (so no skin forms on the pastry cream)
Cool the pastry cream to room temperature, and then chill in the refrigerator.
o assemble- make sure the tart shell is cool and the pastry cream chilled. Fill the tart base with the pastry cream, add the rhubarb pieces and brush with the syrup. Keep the tart refrigerated