Aubrey Plaza was spotted cradling her newborn baby in her first public sighting since giving birth. The actress, 42, sweetly held the little one against her chest as she stepped out with her family in New York City on Sunday. The newborn is the first child for both Plaza and her boyfriend Christopher Abbott, 40. For the warm summer day outing, she wore a black tank top and sunglasses, putting on a casual display as she brought their baby out to Manhattan. Plaza was spotted arriving at the Winter Garden Theatre to support her boyfriend at his final performance of the Broadway revival, Death of a Salesman. She was last pictured with her baby…