Preheat the oven to 325°F (163°C). Grease an 8x8-inch metal brownie pan with pan spray.
In a small bowl, whisk together the flour, baking powder, and salt. Set aside.
In a small saucepan over low heat, combine the olive oil, butter, white sugar, and brown sugar. Stir until the butter is fully melted and the sugars are incorporated. The mixture will look sandy—that's expected.
Remove from heat and add the milk chocolate chips, stirring until melted. The mixture will still appear grainy. Transfer to a medium bowl and let cool for 3-5 minutes until warm but not hot.
Whisk the Dutch-processed cocoa powder (or substitute regular cocoa powder) into the warm chocolate mixture until smooth and lump-free.
Stir in the vanilla extract and eggs, whisking thoroughly until fully combined. Let the mixture rest for 10 minutes to allow the sugar to dissolve further. After 10 minutes, whisk again for 30-60 seconds to ensure a silky batter.
Add the dry ingredient mixture to the wet ingredients and stir gently with a spatula until just combined. Avoid overmixing to prevent toughness.
Stir in the chopped dark chocolate chips until evenly distributed. If desired, sift out any chocolate dust before adding to maintain contrast in the brownie.
Pour the batter into the prepared 8x8-inch metal pan. Do not spread it with a spatula, this will disrupt the brownie skin. Instead, firmly tap the pan on the counter multiple times to level out the batter.
Place the pan in the preheated oven (not using convection) and bake for 35 minutes. For best results, check doneness with an instant-read thermometer (202-205°F/95°C) or a cake tester (it should come out with minimal sticky batter).
Let the brownies cool in the pan for at least 60-90 minutes before cutting. This allows the texture and flavors to fully develop.