Pecan Fudge Sheetcake

My mom made a cake very similar to this when I was young. I always looked forward to that rich chocolate frosting on that cake..when it was warm!!!!
It seemed I could never wait for this cake to cool---I always wanted a piece right when she poured on the frosting :)

1 pkg. Duncan Hines Moist Deluxe Butter Fudge Recipe Cake Mix
1/2 cup butter
1/2 cup plus 2 tablespoons milk
1/4 cup unsweetened cocoa
1 pound powdered sugar
1 teaspoon vanilla
3/4 cup chopped pecans

Preheat oven to 350
Grease 15 1/2 x 10 1/2 inch pan

Prepare cake following package directions for basic recipe.
Pour into pan
Bake on 350 for 20-25 minutes or until toothpick inserted in center comes out clean.

For Frosting:
Place butter, milk and cocoa in medium saucepan
Stir on low heat until butter is melted.
Add powdered sugar and vanilla, stirring until smooth.
Stir in pecans.
Pour over warm cake.
Cool completely.
Do not refrigerate.
Leave covered on table.