Prepare the Pan: Preheat the oven to 350°F. Line a 9×9-inch or 8×8-inch square baking pan with foil or parchment paper, or grease it with baking spray. Set the prepared pan aside.
Melt the Chocolate: Combine the unsalted butter and chopped semi-sweet chocolate in a large microwave-safe bowl or melt them together over a double boiler. If using a microwave, heat in 30-second intervals, stirring after each interval until the mixture is completely melted and smooth. Cool the Chocolate Mixture: Let the melted butter and chocolate mixture cool for 8–10 minutes before continuing.
Add Sugar and Eggs: Add the granulated sugar and eggs to the slightly cooled chocolate mixture. Whisk or stir thoroughly with a rubber spatula until the ingredients are very well incorporated.
Flavor the Batter: Mix in the vanilla extract and espresso powder until evenly combined.
Add the Dry Ingredients: Add the all-purpose flour, salt, baking powder, and unsweetened cocoa powder. Stir until the dry ingredients are fully incorporated and the brownie batter is well combined.
Blend in the Oil: Pour in the canola oil and stir until it is completely incorporated into the batter.
Fold in Milk Chocolate Chips: Add 1 cup milk chocolate chips and stir until they are evenly distributed throughout the brownie batter.
Fill the Pan: Transfer the brownie batter to the prepared baking pan and spread it into an even layer.
Add the Chocolate Topping: Sprinkle ¼ cup semi-sweet chocolate chips over the surface. Use a rubber spatula to gently press the chips into the batter, then smooth the batter so it sits evenly in the pan.
Bake the Brownies: Bake at 350°F for 25–30 minutes, or until a cake tester inserted into the brownies comes out clean with only a few fudgy crumbs attached.
Cool Before Cutting: Allow the brownies to cool before cutting them into squares.
Store the Brownies: Keep any leftovers in an airtight container at room temperature.
