Begin by preheating your oven to 350°F (175°C). Prepare a 9x13 inch baking pan by greasing it lightly with butter or lining it with parchment paper for easy release of the brownies after baking.
In a medium saucepan, melt the unsalted butter over low heat. Stir occasionally to ensure even melting. Once the butter is completely melted, remove the saucepan from the heat and incorporate the granulated sugar. Mix vigorously until the sugar is well combined and the mixture is smooth.
Allow the butter-sugar mixture to cool for a few minutes, then add the eggs one at a time, whisking thoroughly after each addition until fully integrated. Finish this step by stirring in the pure vanilla extract for added flavor.
In a separate mixing bowl, sift together the all-purpose flour, cocoa powder, baking powder, and fine sea salt. This process helps remove lumps and ensures an even distribution of the dry ingredients.
Gradually fold the dry mixture into the wet mixture using a spatula. Combine gently until just incorporated; be careful not to overmix as this can result in a denser brownie.
Carefully fold in the chocolate chips and walnuts (if using), ensuring they are evenly mixed throughout the brownie batter.
Transfer the brownie batter into your prepared baking pan. Use a spatula to spread the batter evenly, smoothing the top for a nice finish.
Place the pan in your preheated oven and bake for 25-30 minutes. To check for doneness, insert a toothpick into the center of the brownies. It should come out with a few moist crumbs clinging to it, but not wet batter.
Once baked, remove the brownies from the oven and let them cool in the pan for at least 15 minutes. They will continue to set as they cool, making them easier to cut.
Notes
For an extra touch, dust the cooled brownies with powdered sugar. Serve each brownie with a generous scoop of vanilla ice cream on the side for an indulgent dessert experience!