Preheat the oven to 175°C/350°F. Spray with oil a 8inch square pan and line with parchment paper. Set the oven rack onto the middle shelf.
In a large microwave-safe bowl, fold in the butter and dark chocolate. Cover the bowl and microwave for 30 seconds, stir the ingredients, then melt for another 30 seconds, until fully smooth and combined.
Stir the sugar and ground espresso coffee into the bowl wioththe butter and chocolate. Then add the vanilla extract and maple syrup. Whisk to combine all the ingredients.
Stir in the eggs, one at a time, wait until each egg is fully incorporated before adding the next one.
Add in the flour, cocoa powder and a pinch of salt, and stir until all the ingredients are JUST combined. Make sure to not overmix the batter!
Transfer the mixture into the prepared pan and spread it evenly, levelling out the top.
Bake for 30-35 minutes (see notes), then insert a toothpick into the centre of the pan. If it comes out very wet, the brownies are not done, if it's just slightly wet, the brownies are done.
Remove the espresso brownies from the oven and allow them to cool on a wire rack, then cut them into squares and serve.
Store leftover brownies in an airtight container for up to 3 days.