Promote That Pawn

White to play and mate in two moves
 

a

b

c

d

e

f

g

h

  

8

 8

7

 7

6

 6

5

 5

4

 4

3

 3

2

 2

1

 1
 

a

b

c

d

e

f

g

h

  

Solution

  1. b8 = N+   Ka5
  2. b4            mate

Note that if white does not promote to a knight and obtain check then black will play h1 = Q+ and white cannot then mate in two