Marshmallow Fudge Bars

INGREDIENTS

• 2 cups white sugar
• 1/4 cup unsweetened cocoa powder
• 1 cup butter, melted
• 4 eggs
• 2 teaspoons vanilla extract
• 1 1/2 cups all-purpose flour
• 3/4 teaspoon baking powder
• 1 teaspoon salt
• 1/2 cup chopped walnuts
• 1 (16 ounce) package miniature marshmallows
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• 1/2 cup brown sugar
• 1/4 cup water
• 1 (1 ounce) square unsweetened baking chocolate
• 1 tablespoon butter
• 1 teaspoon vanilla extract
• 1 1/2 cups confectioners' sugar