Line an 8×4 inch loaf pan with parchment paper and grease. Preheat oven to 160°c.
Combine butter, brown sugar, and maple syrup in a mixer fitted with a paddle attachment and beat on high speed until smooth and fluffy, about 3 minutes.
In a mixing bowl, combine flour blend, cocoa powder, baking powder and bicarbonate of soda, and salt. Whisk until lump free.
With the mixer running on medium speed, add half the flour mixture, then the orange juice, then the rest of the flour mixture. Beat each egg in, one at a time, beating well and scraping down the sides of the bowl after each addition. Add the orange zest and 150g chocolate chips and stir to combine.
Scrape the batter into the prepared pan and bake for 40 – 45 minutes. Let cool in the pan then transfer to a wire rack.
Melt the remaining chocolate chips in a heat-safe bowl over a pot of simmering water. Pour the chocolate over the loaf and top with orange zest if desired.