Preheat the oven to 180°C (160°C fan oven) Gas Mark 4. Roll out the pastry on a lightly floured surface until big enough to line a 22-23cm round deep loose-bottomed tart tin. Line the pastry with foil or greaseproof paper, fill with baking beans and bake for 25 minutes. Remove the paper and beans and cook for 10 minutes more until sandy and golden. Set aside.
Make the filling by putting the cocoa powder, plain flour, almonds, butter, sugar and eggs into a big mixing bowl. Beat with an electric whisk until smooth, then stir in the chocolate chips.
Spread the cherry pie filling over the tart case, then spoon the chocolate sponge mix on top. Scatter over the flaked almonds, then bake for 35-40 minutes until the sponge is risen and firm. Allow to cool completely in the tin.
To serve, lift from the tin and dust with a little icing sugar before slicing.