Preheat oven to 180℃/350℉ degrees. Grease and line an 8” (or 20x20cm) square tin.
Melt together the butter and dark chocolate in a bowl over simmering water, then allow to cool slightly.
In a large bowl, stir together the eggs and sugar. Stir the slightly cooled chocolate mix.
In a medium bowl, whisk the rye flour, cocoa powder, malt powder, baking powder and salt, then mix this into the chocolate/egg mix with a spatula.
Pour this into the baking tin and bake for 26-32 minutes. You’re aiming for the slightest wobble. A cake tester won’t come out completely clean, but the surface of the brownie will look baked. If you have a thermometer, take it out at around 170-180℉.
Allow to cool in the tin at room temperature, before transferring the brownies into the fridge to set overnight.
Cut into 16 pieces and enjoy cold or at room temperature.