Mix cake according to directions on box. While cake is warm, poke holes in top (with handle of wooden spoon). Melt SNICKERS® with 1/2 cup water in microwave. Pour over warm cake, chocolate goes into the holes and nuts stay on top.

Meanwhile, on medium heat, mix milk and flour, whisk until thick like paste; cool. Beat butter, sugar and vanilla until fluffy, add flour mixture and whip; frost cake.