Puzzle | 13 December 2018

White to play. This is a variation from Carlsen-Caruana, World Championship (Game 11), London 2018. Carlsen set a small trap for his opponent in this endgame which Caruana avoided and drew easily. This position shows the trap. How can White win at once? Please note that this is not a prize puzzle. This is because of the Christmas production schedule.
 
Last week’s solution 1 … Bg4