Mix the ground flax seeds and water together to make your flax egg. Set aside to thicken.
Melt the dark chocolate over a bain-marie (a heatproof bowl set over simmering water).
In a large bowl, sieve together the flour, Demerara sugar, baking powder, and a pinch of salt. Mix well to combine.
Melt the coconut oil in a saucepan. Add the melted coconut oil to the flour mixture, followed by the soaked flax eggs, vanilla extract, and non-dairy milk. Beat the mixture thoroughly by hand or with an electric hand mixer.
Add the melted chocolate to the batter and beat again for 2-3 minutes until fully incorporated.
Pour the brownie mixture into a 30 x 20cm baking pan lined with parchment paper, smoothing the top evenly.
Bake in the preheated oven for 30-40 minutes, or until a skewer inserted into the centre comes out almost clean.
Remove the brownies from the oven and leave them to cool completely. Allowing the brownies to cool fully is crucial for them to firm up and achieve the desired texture. This can be the hardest part, but it’s essential if you want the perfect brownie consistency.