Rb4, the only move that keeps an advantage for White. I did not find this move in the game, and lost my advantage in this endgame as White. Analyzing after the game I was fascinated by this move, which is so effective and clean though it may not come to mind at first.

This move x-ray protects the pawn on f4, prevents Black's rook from cutting off White's king along the b-file, and protects itself with the c3 pawn so that White's king is free to move. Beautiful.