Preheat oven to 325°. In large bowl, whisk eggs and vanilla. Whisk in sugar, then butter. Stir in cocoa powder and flour. Pour into parchment-lined 9-by-13- inch baking pan. Bake until a toothpick comes out with moist crumbs attached, 35 to 40 minutes. Let cool. In medium pan, stir chocolate and cream over medium-low heat until melted; mix in zest. Frost brownies, garnish with Dried Orange Slices, and cut into pieces.