Combine first 5 ingredients in a large mixing bowl. Add butter and eggs, stirring until smooth. Stir in 1/2 cup pecans. Pour mixture into a greased and floured 13- x 9-inch baking pan.
Bake at 350° for 25 to 30 minutes or until a wooden pick inserted in center comes out clean. Immediately sprinkle marshmallows over top; return to oven, and bake 1 minute. Remove from oven, and spread marshmallows evenly on top. Let stand 5 minutes.
Spread Chocolate Frosting evenly over marshmallows, and sprinkle with remaining 1/2 cup pecans. Cool completely, and cut into squares.
Note: If marshmallows do not spread easily after 1 min. in oven, do not bake longer. Let stand 1 to 2 min. to soften.