For the frangipane
250g unsalted butter
250g caster sugar
50g plain flour
250g ground almonds
For the crumble 350g plain flour
200g brown sugar
100g caster sugar
Grated zest of 2 lemons
165g unsalted butter
250g hazelnuts, toasted and chopped
500g caster sugar
500g sugar paste
500g rhubarb, peeled and sliced into 1cm chunks
To make the frangipane, cream together the butter and sugar. Beat in the flour and almonds, then the eggs. Prepare the crumble by rubbing together the flour, sugars, zest and butter, then mix in the hazelnuts.
Bring the water and sugar to the boil and blanch the rhubarb for two minutes until tender. Strain and cool. Reduce the sugar solution to a syrup. Roll out the sugar paste to a thickness of 3mm and bake blind a buttered flan case at 170ºC for 10-15 minutes.
Mix the cooked rhubarb with the frangipane and spoon into the tart case. Cook at 160íC for 25-30 minutes until firm to the touch. Sprinkle with the crumble mix and bake at 200ºC for 5-10 minutes until golden.
Serve warm with whipped cream and the rhubarb syrup.