Have shelf in center of oven and preheat to 300 degrees F.
Spread the pecans on a baking sheet and roast for 10 minutes. While the nuts are hot, stir in 2 tablespoons of the butter. When cool, coarsely chop and set aside.
Line a 13 x 9 x 2-inch pan with release foil or parchment. With release foil you won't need extra fat for greasing. If you don't have release foil you can use regular foil and grease the bottom or you can use parchment.
Place the remaining 1 1/2 cups (3 sticks) butter around the edge of a microwave-safe glass bowl. Place the semisweet and sweet chocolate in the center. Melt the butter and chocolate in the microwave on 100% power for 1 minute, stirring at least 2 times, and then 15 seconds more, stirring 1 time. Otherwise, melt in a double boiler or saucepan over lowest heat.
In a large bowl, beat the eggs with a fork just to blend whites and yolks. With a minimum of hand stirring, stir together the eggs, egg yolks, brown sugar, confectioners’ sugar, granulated sugar, corn syrup, vanilla and salt.
By hand, (again with a minimum of stirring), stir together the egg mixture and the chocolate mixture. Stir in the flour. Pour the batter into the prepared pan and smooth out.
Soak cake strips in water and wrap around the outside edge of the pan as directed.
Bake at 300 degrees F until brownies just begin to pull away from the edge of the pan, about 1 hour. Err on the side of undercooking rather than risk drying out the brownies.
Cool completely in the pan or a rack. Remove the brownies from the pan, using the parchment or foil overhang to help lift out the brownies. When completely cool, wrap the brownies well with plastic wrap and refrigerate overnight.
Remove brownies from pan and cut into squares.