Preheat oven to 180°C / 160°C Fan / 350°F / Gas Mark 4. Line a 20cm square cake tin with parchment paper and set aside.
Break the dark chocolate up and add to a small heatproof bowl set over a pan of simmering water (bain-marie) - make sure the base of the bowl is not directly touching the water. Gently melt the dark chocolate until it’s smooth.
In a large mixing bowl, mix the sugar and orange zest together. Now sift together the flour, cocoa powder and baking powder. Give these ingredients a quick whisk together to combine then whisk in the oil, plant milk and orange extract until you have a smooth batter. Whisk in the melted chocolate until incorporated. Finally, if using fold through the extra chocolate chips/chunks.
Transfer the brownie batter to the lined tin.
Bake the brownies for 25-30 minutes - I always bake mine for 25 minutes because I like the brownies extra fudgy. Leave to cool completely in the tin before cutting in to 16 squares. We left ours overnight before cutting.