As New York City’s Garment District struggles to maintain a foothold in the fashion industry, David Gensler, founder of the Keystone Design Union, a Brooklyn-based design consultancy, and apparel label Serum Versus Venom, has it figured out. As the mastermind of Brooklyn Sewn, a new in-house fashion atelier in Williamsburg, Gensler is working to keep the tradition of creating high-quality garments in Gotham alive. By offering everything from pattern-making to small production runs, Gensler is banking on the ethos “if you build it, they will come” — “they” being local designers and brands looking to produce their wares on a small, accountable scale.