My vote would be for any of the peanut related flavors at Doughnut Plant.
Vegan places sometimes feature a chocolate peanut butter cake I've seen listed as a "peanut butter bomb". It's not delicate, let's just put it that way. Teany used to carry it, but I'm not sure the revamped reopened location has it.
90 Rivington St, New York, NY 10002
220 W 23rd St, New York, NY 10011
Some of my favorites:
Big Booty Bread Co., peanut butter cookie
Buttercup Bakeshop, PB&J cupcake
Les Halles, homemade peanut butter ice cream
'wichcraft, peanut butter cream'wich
Big Booty Bread Co.
261 W 23rd St, New York, NY 10011
11 W 40th St, New York, NY 10018
15 John Street, New York, NY 10038
Buttercup Bake Shop
973 2nd Ave, New York, NY 10022
Perhaps, Peanut Butter & Co? We've never been, but the desserts sound delicious.
My favorite upscale peanut butter-inspired dessert is EMP's Chocolaate Palette with Peanut Butter and Popcorn: http://www.flickr.com/photos/11863391@N03/5644044844/in/set-72157626429193975
Eleven Madison Park
11 Madison Ave., New York, NY 10010
Peanut Butter and Co.
240 Sullivan St, New York, NY 10012