While the shortbread is baking, stir together the flour, sugar, cocoa powder, baking powder and salt
Add the rest of the ingredients, except the jam, and mix until well blended
Spread a layer of strawberry jam on top of the warm, baked shortbread then smooth the brownie mixture evenly on top.
Bake for around 25 - 30 minutes until the top is set, the centre soft and the edges start pulling away from the sides of the tin
Remove from the oven and leave to cool in the tray for about 10 minutes before lifting out, using the paper lining
Cut into small squares while still warm, then leave to cool fully on a wire tray
Dust with a mix of icing sugar and cocoa powder or leave plain