Lasker on the Attack

Last time, I left you with this chess position, from Lasker-Steinitz, 1896:

When I ask my students about the opponent's weaknesses in this position, they often correctly identify the pawn on d6 (one attacker, one defender) and the knight on e7 (due to the battery on the e-file). But they have a hard time finding the strong move Lasker played: 30.Bf4!, attacking the pawn on d6 a second time. This move looks impossible, due to 30...Nxf4, so it is very easy to accidentally filter it out. But if you look deeper, White has a crushing reply: 31.Nf6+!, with a discovered attack on the knight on e7. 31...Kd8 32.Rxe7 is winning for White, while 31...gxf6 allows a forced checkmate: 32.Re7+ Kd8 33.Re8+ Kc7 34.R1e7#.

Black's best defense in a tough spot after 30.Bf4 would have been 30...Nf5, bringing up the following position:

What would Lasker have played here? Keep on thinking about the opponent's weaknesses! Solution coming tomorrow.