In a large heavy saucepan, melt butter and chocolate over low heat; stir until smooth. Cool., In a large bowl, beat eggs and sugar on low speed until combined. Beat on medium-high until thickened and lemon-colored, about 12 minutes. Beat in vanilla and chocolate mixture. Fold in flour and salt just until blended (batter will be thick). Fold in walnuts if desired. , Transfer to two greased 13x9-in. baking pans. Bake at 350° for 25-30 minutes or until a toothpick inserted in the center comes out clean. Cool on wire racks for 15 minutes. , In a large saucepan, combine the cream, sugar and butter. Cook and stir until sugar is dissolved. Bring to a boil, without stirring. Reduce heat; simmer, uncovered, for 3 minutes. Cool for 3 minutes. , Place cocoa in a heat-proof bowl. Carefully whisk hot liquid into cocoa until smooth (do not scrape pan). Cut brownies into squares; serve with ice cream and hot fudge sauce. Garnish with whipped cream and cherries if desired.