Preheat your oven to 180°C (356°F). Line an 8x8" square pan with parchment paper and set it aside.
Finely chop the chocolate and add it to a heat-resistant bowl along with the vegan butter. Place the bowl on top of a saucepan that is about ¼ ways filled with simmering water (bain-marie). Stir the chocolate and butter with a rubber spatula every so often to melt it evenly.
Once melted, add the flax eggs, light brown sugar, light muscovado sugar, vanilla extract, and almond milk to the bowl with the melted chocolate and butter. Mix well to combine.
In a separate large bowl, whisk together the ground almonds, cocoa powder, baking powder, and sea salt. Add the wet ingredients to the bowl with the dry ingredients and use a spatula to fold everything together until you have a smooth batter. Be careful not to over-mix.
Gently spread the brownie batter into the base of the tin. Sprinkle the chocolate chips on top (if using).
Bake for 30-35 minutes. To check they're ready, insert a toothpick or skewer, it should come out with a few crumbs on it but not have a tonne of batter.
Allow the brownies to cool completely for 30 minutes to an hour before cutting them into servings.