Heat oven to 350. Line jelly-roll pan with foil; grease foil. Heat butter and chocolate in large saucepan over low heat until melted and smooth. Remove from heat; whisk in sugar and eggs. Stir in flour, vanilla and salt until blended. Stir in walnuts. Pour batter into prepared pan. Bake 25 to 30 minutes until toothpick inserted in center comes out clean. Cool brownies completely on large wire rack. Invert pan onto rack; peel off foil. Invert again onto large cutting board. Cut brownies lengthwise into thirds, then crosswise in 5 pieces. Can be made ahead. Store in airtight container at room temperature up to one week or freeze up to 1 month. Makes