1 Preheat the oven to 180˚C/160˚C fan/gas mark 4. Grease two 17cm deep sandwich tins and line with baking paper.
2 Beat together the eggs, flour, caster sugar, butter and baking powder until smooth.
3 Put the cocoa in a separate mixing bowl and gradually stir in the water to make a stiff paste. Add to this the cake batter, then gently stir in half of the crushed Oreos.
4 Turn the mixture into the prepared tins. Bake for 20-25 minutes, or until shrinking away from the sides of the tin and springy to the touch.
5 Leave to cool in the tin, then turn on to a wire rack to cool completely.
6 Melt the cream and chocolate over a pan of hot water over a low heat. Stir until smooth, then set aside to cool and thicken.
7 To make the filling, combine the cream, icing sugar and vanilla in a bowl and whip until thick. Stir through the crushed Oreos.
8 Sandwich the cakes together with the Oreo cream. Top with the chocolate icing and sprinkle crushed Oreo biscuits on top.