A jury found defendant guilty of aggravated manslaughter of her husband, as a lesser included offense of murder; first degree attempted murder and second degree endangering the welfare of her minor daughter; and second degree endangering the welfare of her minor son. Defendant asserted the affirmative defense of insanity under N.J.S.A. 2C:4-1. The central issue in this appeal concerns the proper assessment of this defense by the jury. This court reverses defendant's conviction and remands the matter for a new trial. As a matter of plain error under Rule 2:10-2, this court concludes that the State's expert witness' testimony usurped the jury's exclusive role to decide defendant's state of mind at the time she committed these offenses, rendering the verdict unsustainable. State v. Simms, 224 N.J. 393, 396 (2016); State v. Cain, 224 N.J. 410, 424 (2016). The trial judge also engaged in ex parte interactions with the pool of prospective jurors before the jury selection process had even begun. Although not outcome determinative, this court also holds that the trial judge's ex parte interactions with the pool of prospective jurors violated defendant's right under Rule 3:16(b) to be present "at every stage of the trial, including the impaneling of the jury," as well as the Supreme Court's holding in Davis v. Husain, 220 N.J. 270 (2014), not to engage in ex parte interactions with the jury at any stage of the trial. See also Rule 1:2-1.