Step 1: In a large mixing bowl, whisk together the glutinous rice flour, all-purpose flour, granulated sugar, baking powder, and salt. Make sure there are no lumps and the dry ingredients are thoroughly combined.
Step 2: In a separate medium bowl, whisk together the gently pressed silken tofu, whole milk, large egg, and vanilla extract until smooth and well combined. Ensure the tofu is fully incorporated and there are no large pieces.
Step 3: Pour the wet ingredients into the dry ingredients. Using a sturdy spatula or a wooden spoon, mix until a shaggy dough begins to form. Once it starts coming together, switch to using your hands to gently knead the dough within the bowl until it forms a cohesive, soft, and slightly sticky ball. Be careful not to overmix.
Step 4: Lightly flour your work surface and your hands. Take small portions of the dough (about 1.5-2 tablespoons each) and roll them into small balls. You’ll need 8 small balls to form one donut. Arrange eight small dough balls in a circle on a small square of parchment paper, gently pressing them together to form a ring shape, like a flower. Repeat with the remaining dough.
Step 5: Prepare your frying station. Pour enough vegetable oil into a deep pot or Dutch oven to reach a depth of about 2-3 inches. Heat the oil over medium heat until it reaches 350°F (175°C). Use a kitchen thermometer to ensure accuracy.
Step 6: Carefully lower the mochi donut rings, along with their parchment paper squares, into the hot oil, one or two at a time, depending on the size of your pot. The parchment paper will peel off easily after about 30 seconds. Use tongs to remove the parchment. Fry the donuts for 2-3 minutes per side, or until they are beautifully golden brown and puffed. Flip them gently to ensure even cooking. Once fried, transfer the donuts to a wire rack set over a baking sheet to drain excess oil.
Step 7: While the donuts are cooling slightly, prepare your glaze. In a bowl, whisk powdered sugar with 2-3 tablespoons of milk or water until smooth. Add more liquid sparingly if needed, until you reach a pourable but not too thin consistency. Dip the warm Mochi Donuts into the glaze, letting the excess drip off, then place them back on the wire rack to set.