Cream the butter and sugar with the oil and vanilla essence until light and creamy, add the egg and beat well.
Sift together the flour, baking powder and salt and add to the creamed mixture, working the mixture into a dough. Halve the dough and place one half in the freezer for 30 minutes or until frozen.
Press the unfrozen dough evenly across the bottom of a greased cake pan. Spread the dough with all of the Rhodes Strawberry Jam. Grate the frozen dough over the top of the jam, and bake in a preheated oven at 180 °C for 40 minutes or until golden and crunchy.
Remove from the oven, allow to cool and dust generously with icing sugar before serving.