Heat the oven to 175 C / 350 F. Line a 20 cm / 8-inch square baking pan with parchment, leaving an overhang on two sides so you can lift the brownies out later.
Melt the butter and chopped chocolate in a 2-quart / 1.9 L saucepan over low heat, stirring, for 3 to 4 minutes until smooth. Take it off the heat and let it cool for 2 minutes so it won't cook the eggs.
Whisk in the coconut sugar for 1 minute, then add the eggs one at a time. Stir in the vanilla and milk until the mixture looks glossy.
Sift the coconut flour, cocoa powder, baking powder, and salt over the saucepan. Whisk for 1 minute until no dry streaks remain. The batter will be thick. Fold in 40 g of the chocolate chips.
Scrape the batter into the pan and press it into the corners with a damp spatula, smoothing the top. Scatter the remaining 20 g of chips over the surface.
Bake for 25 to 28 minutes, until the edges are set and a toothpick in the center comes out with a few moist crumbs and no wet batter. The center should still look slightly soft.
Cool the brownies in the pan for 30 minutes. Lift the slab out by the parchment and cut into 16 squares, about 5 cm each, wiping the knife between cuts.