Adjust the oven rack to the lower third position, just below the center of the oven, and heat the oven to 350°F. Line an 8-inch square pan with parchment paper or aluminum foil, leaving a 1-inch overhang on all sides. Spray lightly with nonstick spray and set aside.
In a medium heatproof bowl set over a pot of barely simmering water, melt the chocolate and butter, stirring constantly until the mixture is smooth. You can also microwave in 30-second intervals, stirring between each one.
Remove from heat and whisk in the cocoa powder. Set aside to cool slightly.
In a separate bowl, whisk the egg and sugar, vanilla, and salt together until well combined and the mixture is frothy.
Add the warm chocolate mixture and whisk until well combined.
Add the flour and use a silicone spatula to fold the batter together until no visible streaks of flour remain.
Spread the mixture evenly into the prepared pan and bake for 20-25 minutes, or until the top of the brownies look dry and the edges begin to pull away from the sides of the pan.
Make the topping
Whisk the sugar, butter, milk, and vanilla together until well combined. Stir in the pecans.
Spread the topping evenly over the brownies and bake for 15 minutes longer.
Cool the brownies in the pan on a wire rack for 2 hours. Lift the brownies out of the pan by the foil overhang. Cut into square and serve. I like to refrigerate them for 45-60 minutes before cutting as this makes it easier to get clean slices. Be sure to use a sharp knife that will easily slice through the pecans.
Notes
Chocolate: You can use bittersweet or semisweet baking chocolate. Avoid chocolate chips, they don’t melt as smoothly as bar chocolate.
Cocoa powder: You may use regular cocoa or Dutch-processed.
Flour: Make sure to measure the flour correctly! Accidentally using too much flour will cause the brownies to be dense and hard.
Pecans: You can use any other nut you prefer!
Don’t overbake! Overbaking will cause the brownies to be dry. It’s best to remove them a few minutes early during the first bake. Don’t wait for a toothpick to come out clean.
Make Ahead Tip
Brownies can be stored at room temperature in an airtight container for up to 1 week.
Brownies can be frozen for up to 3 months. Thaw in the refrigerator overnight and bring to room temperature before serving.