Preheat oven to 350℉/177℃.
Spray a 9x13- or an 8×8-inch baking pan (for thicker brownies) with oil spray and line with parchment paper. Leave a 2-inch overhang on both sides to lift the brownies out easier after they cool. Then grease the parchment paper with baking spray. Set the pan aside.
Combine the chocolate chips or chunks and butter in a medium bowl. Then melt in the microwave, stop, and stir frequently every 20-30 seconds so it doesn't scorch or burn. It usually takes about 2 minutes. Stir the chocolate continuously until it is smooth, shiny, and completely melted. If the microwave is not your thing, then melt in a double broiler over medium heat, stirring occasionally until melted.
Whisk the eggs in a large bowl.
Whisk sugar, brown sugar, vanilla, and salt in until combined.
Stir in melted chocolate, then gently fold in the flour and cocoa powder until thoroughly mixed. Pour batter into prepared pan and spread evenly. Pre-bake for 25–35 minutes or until slightly ready.
While the brownies are pre-baking, prepare the pecan pie filling.