One of the secrets is to under cook the brownies lightly so they are not too firm, with that soft but joyously chewy texture.
Butter a pan 9 inches square by 2 inched deep and dust it with flour. Set your oven for 350 degrees.
Melt 4 ounces (that's 4 squares) of unsweetened chocolate over hot water and when it is melted, stir in 1 cup (1/2 pound) softened butter, piece by piece, that way it blends in easily. Remove from the heat and add 2 cups of sugar, 3 rather lightly beaten eggs and 2 teaspoons of vanilla. Mix well. Now stir in 1 to 1 1/4 cups of chopped walnuts or pecans, depending on your preference (walnuts are more traditional). Gradually add 1 cup of sifted all purpose flour and mix it quite well. Pour the batter into the prepared pan and bake at 350 degrees for about 40 to 45 minutes or a little longer, but don't let the brownies get too well done or they won't be chewy and gooey. Cool in the pan, on a cake rack, before cutting into squares.