Preheat the oven to 350 degrees F (175 degrees C). Grease and flour an 8x8- or 9x9-inch baking pan.

Beat together sugar and butter in a medium bowl. Add eggs and mix well. Combine flour, cocoa, and salt; stir into sugar mixture. Mix in vanilla, then stir in walnuts. Spread evenly into the prepared pan.

Bake in the preheated oven until edges are firm, 25 to 30 minutes. Cool before cutting into squares.