For the orange slice, beat the eggs and sugar until very foamy, mix the flour and baking powder and add to the foamy mixture with the water and oil.
Spread on a buttered and floured baking sheet and bake for about fifteen minutes to 20 minutes in a preheated oven. Let cool.
Make a custard with the orange juice and sugar and pudding powder, add the butter to the hot mixture and stir until melted.
Let cool a bit, then spread the mixture evenly on the pastry base. Let cool. Then whip the whipped cream with the cream stiffener until stiff and spread it carefully and evenly over the pudding mixture.
Place the cookies close together on top of the whipped cream and cover with icing. Refrigerate for a few hours.