Preheat your oven to 350°F (175°C) and prepare an 8x8 or 9x9 inch baking pan lined with parchment paper.

Sift together 1 cup of all-purpose flour, 1/2 teaspoon of salt, and 1/2 cup of cocoa powder in a mixing bowl.

In a medium saucepan over medium heat, combine 1/2 cup of unsalted butter, 1/4 cup of canola oil, and 1/2 cup of granulated sugar. Stir frequently until melted and smooth.

In a separate bowl, whisk together 2 large eggs, 1 egg yolk, and 1 cup of granulated sugar until thick and light in color, then stir in 1 teaspoon of vanilla extract.

Gradually pour the warm butter mixture into the egg mixture, whisking constantly.

Gently fold the sifted dry ingredients into the wet mixture using a spatula.

Fold in 1 cup of semi-sweet chocolate chips and any optional mix-ins like M&M's or nuts.

Pour the brownie batter into the prepared pan and smooth the top evenly.

Bake for about 30 minutes in a 9-inch pan, or 40 minutes in an 8-inch pan. The edges should be firm and the top shiny and crackly.

Let the brownies cool in the pan for about 2 hours before lifting out using the parchment overhang and cutting into squares.