In a bowl, combine the peanut butter and sweetened condensed milk. Refrigerate for 15 minutes. The mixture will be a bit sticky at first but once you refrigerate it, you can shape the mixture into balls with your hands.
In a nonstick pan, whisk together the glutinous rice flour, sugar, and water. Put it over medium heat. Use a rubber spatula to constantly stir until the mixture becomes very thick and forms a dough, about 5-7 minutes. Remove from the heat and let cool for 10 minutes.
Dust your work surface with cornstarch. Place the dough on the work surface and dust with more cornstarch. Roll it into a ¼-inch thick rectangle. Dust off any excess starch from the surface of the dough. Cut the dough into 8 pieces.
Using your hands, scoop a tablespoon of the peanut butter filling and shape it into a round ball. Place it in the center of a piece of dough. Pull the sides of the dough over top of the filling and pinch to seal. Use a dough scraper to chop off excess dough. Place seam-side down on cornstarch and repeat with the rest.
You can eat these right away but I really love to freeze them for an hour until they firm up. Enjoy!