1. Preheat the Oven and Prepare the Pan:

• Preheat your oven to 175°C (350°F).
• Line an 8×8-inch square baking pan with parchment paper, leaving some overhang for easy removal.

2. Combine the Dry Ingredients:

• In a medium bowl, sift together the all-purpose flour, cocoa powder, baking powder, and salt.
• Whisk to combine and set aside.

3. Melt the Chocolate and Butter:

• In a heatproof bowl, melt the dark chocolate and butter together over a double boiler or in the microwave using 20-second intervals. Stir until smooth.
• Let the mixture cool slightly.

4. Beat the Eggs and Sugars:

• In a large mixing bowl, beat the eggs, caster sugar, and demerara sugar with an electric mixer on medium speed until pale and frothy, about 2–3 minutes.
• Mix in the vanilla extract briefly.

5. Combine Wet Ingredients:

• Using a spatula, gently fold the melted chocolate and butter mixture into the egg and sugar mixture. Mix until smooth and glossy.

6. Incorporate the Dry Ingredients:

• Gradually add the dry ingredients to the wet mixture, folding gently with a spatula to avoid overmixing. The batter should be thick but fully combined.

7. Add Chocolate Chips:

• Fold in the chocolate chips, ensuring they’re evenly distributed throughout the batter.

8. Bake:

• Pour the batter into the prepared baking pan and spread it evenly with a spatula.
• Bake for 25–30 minutes, or until a toothpick inserted near the center comes out with a few moist crumbs (not wet batter).

9. Cool and Slice:

• Allow the brookie bars to cool completely in the pan.
• Use the parchment paper overhang to lift the bars out of the pan and onto a cutting board.
• Slice into squares and serve!