Instructions

1. Divide 15 ounces red bean paste into 12 portions (about 2 tablespoons or 34 grams each) and place on a parchment paper-lined plate or small rimmed baking sheet. Roll each portion into a smooth ball. Loosely cover with plastic wrap and refrigerate while you prepare the mochi.
2. Whisk 2 cups glutinous rice flour, 1 3/4 cups water, 1 tablespoon granulated sugar, and 1/4 teaspoon kosher salt together in a large bowl until smooth. Lightly dust a cutting board or silicone baking mat with cornstarch.
3. Pour the rice flour mixture into a large nonstick frying pan and heat over medium heat. Cook, stirring constantly and scraping the edges with a heatproof flexible spatula, until a thick and putty-like mixture forms into a single mass that’s hard to move around the pan, 4 to 5 minutes. Transfer onto the cornstarch-dusted work surface. Let cool completely, about 30 minutes.
4. Dust the top with a little more cornstarch. With the help of a dough or bench scraper, gently knead the dough until smooth, about 1 minute. If at any time the mochi is too sticky to handle, dust with a little more cornstarch. Dust a rolling pin with cornstarch and roll out the mochi until it's a rough 9x12-inch rectangle that’s a scant 1/2-inch thick. Dust the bench scraper with cornstarch and use it to cut the mochi into 12 (3-inch) squares.
5. Working with one piece of mochi at a time and using cornstarch-dusted hands, place a portion of red bean paste in the center of the mochi square and gather the edges together. Pinch to seal, making sure the red bean paste is completely enclosed. Lightly dust with cornstarch when needed (avoid using a lot of cornstarch), but having the edges sticky will better seal the mochi. Gently form the mochi into a smooth round between your palms. Return to the parchment or place in a paper cupcake liner.
6. Loosely cover the mochi with plastic wrap. Refrigerate for at least 2 hours for the best texture and serve chilled.