1Place pecans in a single layer on a baking sheet.
Bake at 350 for 8-10 minutes or until toasted.
2Microwave 1 cup butter and semisweet chocolate in a large microwave-safe glass bowl at HIGH 1 minute or until melted and smooth, stirring every 30 seconds.
3Whisk sugar, flour, cocoa, eggs,vanilla and salt into chocolate mixture. Pour into a greased 15x10x1 inch jelly-roll pan.
Bake at 350 for 20 minutes. Remove from oven and sprinkle evely iwth ninature marshmallows; bake 8-10 minutes or until golden brown.
Drizzle warm cake with chocolate Frosting, and sprinkle evenly with toasted pecans.
Stir together butter, cocoa and milk in medium saucepan over medium heat until butter is melted. Cook, stirring constantly, 2 minutes or until slightly thickened; remove from heat. Beat in powdered sugar and vanilla at medium-high speedf with an electric mixer until smooth.