• Pre-heat your oven to 180℃ Fan/395℉. Line an 8" Square Pan with greaseproof paper.
• In a small bowl, break up the dark chocolate and melt in the microwave in 20 second intervals, stirring in between to make sure it doesn't burn. Alternatively, set up a double boiler. Do this by placing a heatproof bowl over a small pot of simmering water. Add the chocolate to the heatproof bowl and stir until melted. 
• In a large mixing bowl, whisk together melted butter and both sugars. With an electric/stand mixer, go for a solid 3-5minutes so it is totally combined. Add in the eggs and vanilla and mix again.
• Now, add the melted chocolate slowly and combine once again. 
• Add the flour and cocoa powder, fold gently into the wet mixture with a rubber spatula or wooden spoon until just combined. Pour into the lined tin. 

Make the Crumble Topping

• In a bowl, combine all crumble ingredients and mix together into a sand-like mixture. Sprinkle evenly over the brownies. Bake 30-35 minutes. Let cool.

Make the Glaze

• To make the glaze, combine the ingredients in a small bowl/jug. Whisk until smooth then pour over the brownies (if you want this to be runnier/thicker, adjust milk quantity accordingly - more milk for runnier glaze).
• Slice and Serve!