At Rice & Miso in Boerum Hill, Brooklyn, the most distinctive Japanese rice ball filling is a savory paste made from miso, garlic and onion that tastes electric, like a current rippling across your tongue. When the grip of salt subsides, the flavor takes a different shape: a fruity, almost floral, sweetness that reminded me of Muscat grape. Not the fruit, but the grape-flavored Kasugai gummies from Japan. Mika Hatsushima, 46, is the owner of Rice & Miso and a former model from Tokyo. She left one bustling city for another when she moved to New York in 1999. “As a model, my diet was messed up,” she said. “When I got pregnant, my mom came to help me, and she cooked for me.” That’s when Ms. Hatsushima realized that the foods she had grown up eating, like rice balls and bento boxes, were what she wanted to make for her own daughter. In 2012, two years after the first of her two daughters was born, Ms. Hatsushima started selling rice balls and miso soup at the Brooklyn Flea in Fort Greene, Brooklyn. But she tired of the food-market circuit, and opened the Boerum Hill shop in 2017. (She maintains a kiosk at the Archway in Dumbo, and since November has occupied a small grab-and-go storefront in that neighborhood.) ImageA handful of rice balls are pan-seared and basted with a tamari and mirin reduction, which caramelizes against the heat. A handful of rice balls are pan-seared and basted with a tamari and mirin reduction, which caramelizes against the heat.Credit...Caitlin Ochs for The New York Times “It’s mom’s food made with love,” she said. It’s also health food. In Japan, rice balls — known as onigiri or omusubi — are typically cushiony orbs of fluffy white rice with a sheet of nori folded around them. At Rice & Miso, the rice is brown and nutty. This might be why the tuna-mayo version is so popular. Chunks of albacore tuna mixed with dollops of mayonnaise and plenty of salt is an easy-to-love foil to the ascetic brown rice. ADVERTISEMENT Continue reading the main story Other potent fillings also do well: A swipe of ume, or pickled plum, is punishingly sour and salty, and bits of miso-marinated beef are exceptionally sweet. A few grilled rice balls are pan-seared and basted with a tamari and mirin reduction. When the glaze caramelizes, it’s like leveling up on umami. You have 1 free article remaining. Subscribe to The Times Ms. Hatsushima relies on fermented ingredients, some of which she makes herself. One workhorse condiment made in-house is salt koji, a porridge-like mash of salt, water and a bacteria-infused rice called rice koji. To the naked eye, rice koji looks like a jumble of brittle, broken grains. But what it lacks in beauty, it makes up in efficacy — catalyzing the fermentation that results in deep, delicious flavors. At the restaurant, salt koji is the basis of a sauce that snakes across blocks of deep-fried tofu, available as part of a bento box. The tofu itself is remarkably good, fried until the potato starch batter turns simultaneously crisp and glutinous, but the sauce adds a spectrum of flavor from sugary-sweet to inexplicably meaty. In another bento, salt koji is a marinade for chicken, perhaps the best possible brine. Editors’ Picks ‘I Only Drink My Coffee Black, and I Cannot Drink It With Sugar’ He Saved His Last Lesson for Me Matthew Broderick and Sarah Jessica Parker Spend the Night Together Image The restaurant is small and intentionally spare. White-washed walls and high ceilings give an illusion of space. The restaurant is small and intentionally spare. White-washed walls and high ceilings give an illusion of space.Credit...Caitlin Ochs for The New York Times