here is one I used.
It tastes very good but I am still not completely satisfied with it.
It kinda hardens and then is hard to spread and smooth out.
It works very well for a filling. (I did not add the pecans)
Let me know what you think or if you found a better one
1/4 cup butter or stick margarine
1/2 cup dark brown sugar
6 tablespoons evaporated fat-free milk
2 teaspoons vanilla extract
3 cups powdered sugar
1/4 cup chopped pecans
Melt butter in a medium saucepan over medium heat. Add brown sugar. Cook 3 minutes; stir constantly with a whisk. Add milk, 1 tablespoon at a time; cook 3 minutes, stirring constantly. Cool. Stir in vanilla. Combine butter mixture and powdered sugar in a bowl; beat at high speed of a mixer until smooth. Frost cake as directed; sprinkle with pecans.
Note: If it's too thick, add 1 tablespoon evaporated fat-free milk.
Yield: 2 cups