1. Place pecans in a single layer on a baking sheet.
2. Bake at 350° for 8 to 10 minutes or until toasted.
3. Microwave 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.
4. Whisk sugar and next 5 ingredients into chocolate mixture. Pour batter into a greased 15- x 10- x 1-inch jelly-roll pan.
5. Bake at 350° for 20 minutes. Remove from oven, and sprinkle evenly with miniature marshmallows; bake 8 to 10 more minutes or until golden brown. Drizzle warm cake with Chocolate Frosting, and sprinkle evenly with toasted pecans.
Kitchen Express Mississippi Mud Cake: Prepare pecans as directed. Substitute 2 (17.6-oz.) packages fudge brownie mix for batter. Prepare mix according to package directions; pour batter into a greased 15- x 10- x 1-inch jelly-roll pan. Bake at 350° for 25 minutes. Remove from oven, and top with marshmallows; bake 8 to 10 more minutes. Proceed with recipe as directed. Note: For testing purposes only, we used Duncan Hines Chocolate Lover's Double Fudge Brownie Mix.
Caramel-Peanut Mississippi Mud Cake: Omit pecans. Prepare and bake Mississippi Mud Cake as directed. Microwave 1/2 cup bottled caramel sauce at HIGH 15 seconds. Drizzle over browned marshmallows. Drizzle with Chocolate Frosting, and sprinkle with 1 cup dry-roasted peanuts.
Mississippi Mud Cupcakes: Prepare pecans and Mississippi Mud Cake batter as directed. Spoon batter evenly into 24 paper-lined muffin cups. Bake at 350° for 20 minutes or until puffed. Sprinkle evenly with 2 cups miniature marshmallows, and bake 5 more minutes or until golden. Remove from oven, and cool cupcakes in muffin pans 5 minutes. Remove cupcakes from pans, and place on wire rack. Drizzle warm cakes evenly with 1 1/4 cups Chocolate Frosting, and sprinkle with toasted pecans. Reserve remaining 3/4 cup frosting for another use. Note: To serve remaining Chocolate Frosting over pound cake or ice cream, microwave reserved 3/4 cup Chocolate Frosting in a medium-size microwave-safe glass bowl at HIGH 15 seconds or until warm.