Preheat the oven to 180°C.
Cream the butter and sugar together by hand or in a mixer.
Add eggs and beat for several minutes before mixing in the flour.
Flatten the pastry into a round, wrap in paper, and chill for at least one hour.
Roll the pastry to 3mm thickness and line a 21.5cm square tin with two-thirds of it.
Place the rhubarb in the pastry base and sprinkle with sugar.
Cover with a pastry lid, seal edges, brush with egg wash, and bake for 45 to 60 minutes.
Cut into squares, sprinkle with caster sugar, and serve with cream and Barbados sugar.