Tip your sugar into a large mixing bowl
Zest the orange directly into the bowl with the sugar, then mix briefly to combine
Add in your butter and beat until completely softened and slightly fluffy
Sift in the flour and add in the chocolate chips. Beat again until your mixture starts to form large clumps.
Tip your mixture out onto your work surface and gently squeeze to bring the dough together
Once your dough has come together, lightly flour your work surface, then place the dough on and lightly flour the top of it
Using a rolling pin gently flatten and roll out to about 1cm thickness
Cut out circles with a round cookie cutter, 6cm in diameter
Put cut out cookies on a baking tray
Chill for an hour in fridge
When your dough has been chilling for 45 minutes, turn your oven on to 160°C to preheat it
Bake the biscuits for 13-15 minutes until the edges feel firm and the middle is still slightly soft when pressed gently
Cool on your tray for a few minutes, then transfer to a cooling rack to cool completely
As an optional decoration, melt the extra chocolate and drizzle over the top of each biscuit, then finish with an extra grating of orange zest