Pawn promotion with tempo!
1.h4
a5
2.h5
a4
3.h6
a3
4.h7
a2
5.h8Q+
Pawn is promoted to Queen and immediately gains a tempo by giving a check..While Black has to fix up the check first, it becomes White's turn again!
5...Kb7
6.Qb2+
Kc6
7.Qxa2
from here White will checkmate in eight moves against any defense. *