Pour boiling water over dates in a small bowl, and let stand until cool.
Measure flour, baking powder, bicarb, salt and nuts into a small bowl. Stir to mix.
Cream 50g of the butter and caster sugar together in a mixing bowl; beat in egg and vanilla. Add flour mixture to creamed mixture in three parts alternately with date mixture in two parts, beginning and ending with dry mixture. Spread mixture into a greased 22x33cm tin.
Bake at 180 C / Gas 4 for 30 to 40 minutes, or until an inserted wooden skewer comes out clean.
Coconut topping: Mix coconut, dark brown soft sugar, 90g butter and cream in a small saucepan over medium heat. Boil for three minutes. Spread over warm cake, and brown under the grill.