Preheat oven to 350 degrees F. Prepare a greased and floured baking pan.
In a double boiler or in a bowl set over a pan of hot water, melt the chocolate; set aside to cool.
In a bowl, mix together butter and sugar until creamy. Add eggs, one at a time, to the creamed mixture.
In a separate bowl or on wax paper, sift the flour with the salt.
Add the melted chocolate to the egg mixture. Fold in the flour. Stir in the vanilla extract and chopped walnuts. Pour mixture onto the prepared baking pan.
Bake approximately 20 minutes or until an inserted toothpick is clean. Remove from oven.
Let cool and then cut into 2-inch squares to serve.
Katherine Hepburn's Brownie Recipe: https://whatscookingamerica.net/EllenEaston/Broadway-Teatime-Rituals.htm