Combine butter, brown sugar, white sugar, vanilla and egg until well combined. Stir in the flour and the bicarb soda (dough will be stiff).
Pat dough onto an ungreased 30cm pizza tray or on a baking tray.
Bake at 180 degrees C for 15 minutes or until golden brown. Remove biscuit base from oven and let it cool.
In a saucepan heat the chocolate chips, remaining butter and milk over very low heat. Stir until chocolate is melted. Remove the chocolate mixture from the heat and stir in the icing sugar. Beat until smooth, glossy and of spreading consistency. If icing is not glossy stir in a few drops of hot water. Spread over the top of the baked and cooled biscuit.
Immediately sprinkle with pecan halves, Smarties and coconut. Press lightly into icing. Drizzle top with the melted white chocolate. Let stand until set. Remove from tray if desired. Cut into wedges.