• An hour before starting, set out three eggs and 8 tablespoons (1 stick) of butter at room temperature. The softened butter will be used for the frosting.

Brownies

• Preheat oven to 350 degrees. Line a 9x13 pan with foil, leaving a bit of foil overhanging on each end to use as handles later. Grease the foil with cooking spray. (Or use a nonstick 15.2x8 brownie pan without foil.)
• Place 12 Tablespoons of cold butter in a glass bowl (or other microwave-safe bowl). Break up the chocolate bar and add it to the bowl. Heat the butter and chocolate in the microwave, lightly covered, for 1 ½ minutes on high. Add another 30 seconds if the chocolate looks like it's not melted enough. Stir with a silicone spatula until the chocolate fully melts.
• Stir in the white and brown sugar, then add the eggs and vanilla. Mix with a spoon or spatula until blended. Add the flour and pecans (if using) and stir until the batter is mixed, without any streaks of flour showing. Make sure to scrape along the bottom of the bowl to stir. Pour the batter into the pan. (If using a brownie pan that comes with dividers, insert the dividers after you pour in the batter.)
• Bake for 22-25 minutes. Test to see if the brownies are done by inserting a toothpick in the center. The toothpick should come out with fudgy crumbs. If the toothpick is wet, bake the pan of brownies for a few extra minutes and test again.
• Let the brownies cool in the pan. Then lift them out with the foil handles, and frost before cutting into servings. (If you used the brownie pan that comes with the dividers, remove the dividers before frosting the brownies.)

Frosting

• While the brownies are baking, use an electric mixer to cream the room-temperature butter, cocoa, and salt, starting on low and then increasing to medium speed. Add the powdered sugar and mix on low. Add in the milk and vanilla extract.
• Increase the speed to medium-high, and beat the frosting until smooth and fluffy. Cover and refrigerate it until the brownies have cooled. Spread the frosting evenly onto the cooled brownies. (See notes.)
• For the best, moist texture, chill the frosted brownies in the fridge or freezer. Store them in the refrigerator for 3-5 days or freeze them for up to three months. They can be left at room temperature for two days, if you wish.