Shortbread Crust: Butter a 9 inch tart pan. Preheat oven to 375F.

Whisk dry ingredients and add the butter using a food processor or a pastry cutter. Combine until crumbly. Pour into tart case and press into sides. Prick bottom with fork. Cover with parchment paper and baking beans and freeze for 30 min.

Put the rhubarb in one layer in a roasting pan. Mix sugar and juice and pour over.

Bake rhubarb and crust together 13 min and set on wire rack to cool. Blend leftover pastry with an egg and brush on the bottom to seal. Bake again for 5 min and cool again.

Custard: combine cream and sugar and heat until almost boiling. Remove from heat and add vanilla.

Beat the eggs yolks in a mixing bowl. Strain hot cream through a sieve into the egg yolks, whisking constantly until combined

Place tart in oven. Strain the custard mixture into the tart case and bake for 20–30 minutes, or until just set with a slight wobble in the middle. Remove and cool completely. Arrange rhubarb on top decoratively.