This is a strong gambit line against the Nimzo-Larsen which I first came across a while ago when watching Hikaru's blitz games. For those thinking this is just another coffeehouse chess opening, rest assured that it's fully playable and engine-approved—in fact, Leela evaluates the best variations as *very* close to 50.0%, which is what you'd expect from Nimzo-Larsen mainlines.
This study only applies to the standard Nimzo-Larsen development scheme of b3, Bb2, e3, Bb5—meaning the Hippopotamus or other side setups will not be covered.