Preheat the oven to 180C/350F and line a large baking tray with grease proof paper.
Place the oil, sugar, egg and vanilla extract into a large bowl and whisk until well combined and slightly frothy.
Add in the melted chocolate and mix until everything is well combined.
Add in the flour, cocoa powder, baking powder and salt and mix until there are no lumps of flour and everything is smooth and combined.
Tip the batter onto your prepared baking tray and spread with a small angled spatula to 1/4-1/2 inch thickness. If you don't have large baking trays, I would advise you split the mixture between two smaller baking trays to ensure the Brownie Brittle is thin enough.
Once spread, sprinkle the batter with chocolate chips. Place in the oven for 20-25 minutes, until the top is crackly and firm to the touch and the edges are crisp. Mine, at 1/4 inch thickness, took 23 minutes. If you're using two trays, keep a close eye on it and check around 15 minutes.
Remove from the oven and score with a pizza wheel/long knife. I cut diagonally both ways and ended up with around 24 pieces, 2 inches across. Leave to cool before breaking up into pieces and enjoying.
Brownie Brittle will keep in an airtight container or Ziploc bag, at room temperature for 2 weeks.