Melt butter and chocolate in the top of a double boiler, whisking until smooth. Cool to room temperature.
Make Mixture 2:
In a medium bowl, combine sugar, eggs, and vanilla extract.
Make Mixture 3:
Stir together the flour and salt.
Finish and Bake:
Add Mixture 1 to bowl containing Mixture 2, stir to combine, then fold in Mixture 3.
Pour batter into an 11x7-inch rectangular dish. Bake for 35 - 40 minutes until top is set and flaky. You may use an 8-inch square dish for thicker brownies or a 9x13-inch rectangular dish for thinner brownies. Adjust baking time to longer for the smaller pan or shorter for the larger pan.
Notes
You may use 12 ounces bittersweet chocolate in place of the 8 ounces unsweetened chocolate, but reduce the sugar from 2 cups to 1 ½ cups. To elevate the chocolate flavor, you may add 1-3 teaspoons espresso powder to Mixture 1 while the butter and chocolate are melting. You're Gonna Bake It After Allbakeitafterall.com