How to Make It
In a bowl, whisk the mayonnaise, mustard, vinegar and garlic. Gradually whisk in 1/2 cup of the oil. Season with salt.
Spread the flour and panko in 2 separate shallow bowls. In a third bowl, beat the eggs and water. Season the lamb with salt and pepper, then dredge in the flour, tapping off any excess. Dip the floured cutlets in the egg and then coat with the panko.
In each of 2 large skillets, melt 1 tablespoon of the butter in 1 tablespoon of the remaining oil. Add the cutlets and cook over high heat until golden, 3 minutes. Turn the cutlets and cook for 2 minutes. Serve with the aioli.