Melt the vegan butter, and measure ½ cup. I do this by microwaving the vegan butter in a glass measuring cup, in 30-second intervals, until melted.
In a large bowl, whisk the melted vegan butter and sugars together. Add the flax eggs and vanilla, whisk until evenly combined.
Over the same large bowl, sift in the flour and cocoa powder. Add the salt and baking powder and stir with a large wooden spoon until just combined, do not over mix.
Fold in half of the chocolate chips. Pour the batter into a lined 7 x 11 pan with parchment paper and smooth out the top with a spoon or your hands. Sprinkle the rest of the chocolate chips on top of the batter.
Bake 350 degrees F for 35-40 minutes. The brownies may still be bubbling and not look done, but they will firm up a lot as they cool.
Let cool in the pan for at least 20-30 minutes.