For the pastry base:
1) Preheat the oven to 180°C/gas mark 4. Beat the butter and granulated sugar in the bowl of an electric mixer fitted with a paddle attachment, until light, approximately 3 minutes. Add the eggs and the vanilla to the batter and mix well.
2) Meanwhile, sift together the flour, baking powder and salt. Mix the dry ingredients into the batter with the mixer on low speed until just combined.
3) Press the pastry evenly into an ungreased 45cmx30cmx2cm deep baking tin, making an edge around the outside. It will be very sticky so sprinkle the dough and your hands lightly with flour. Bake for 15 minutes, until the pastry is set but not browned. Allow to cool.
For the topping:
1) Combine the butter, honey, brown sugar and zests in a large, heavy-bottomed saucepan. Cook over low heat until the butter is melted, using a wooden spoon to stir. Raise the heat and boil for 3 minutes.
2) Remove from the heat. Stir in the cream and pecans. Pour over the pastry, trying not to get the filling between the pastry and the pan.
3) Bake for 25 to 30 minutes, until the filling is set. Remove from the oven and allow to cool. Wrap in clingfilm and refrigerate until cold. Cut into bars. Dip one end of each biscuit into the melted chocolate, if desired, and serve.