In a large bowl, sift or whisk together 2 cups glutinous rice flour, 1 cup granulated sugar, 1 tsp baking powder, and 1 tsp fine salt until evenly combined and free of lumps.

Combine wet ingredients

In a separate bowl, whisk together 1 cup whole milk, 2 large eggs, 3 tbs melted unsalted butter, and 1 tsp vanilla extract until homogeneous.

Form batter

Gradually pour the wet mixture into the dry ingredients, stirring with a spatula or wooden spoon until a smooth, slightly thick batter forms. The batter should be thicker than a pancake batter but still pourable; if too thick, add up to 2 tablespoons more milk. Rest the batter 10 minutes to hydrate the glutinous rice flour — it will become a bit more elastic and glossy.

Optional Filling / Add-ins

Prepare filling (if using)

If using a filling like sweetened red bean paste or custard, divide it into 12 equal portions of about 1 tablespoon each and keep them covered so they don't dry out. Toast sesame seeds or peanuts in a dry skillet over medium heat for 2–3 minutes until fragrant; set aside to cool.

Incorporate add-ins (alternate)

If you prefer studded donuts rather than filled, gently fold 1/2 cup of the chosen add-in (e.g., mashed sweet red beans or chopped nuts) into the batter before frying.

Shaping and Frying

Heat oil

Pour about 3–4 cups neutral oil into a deep skillet or pot to a depth of about 1.5–2 inches. Heat over medium heat to 350°F (175°C). If you don't have a thermometer, test with a small drop of batter — it should sizzle and rise steadily without browning instantly.

Shape plain donuts

For plain rice donuts: lightly oil your hands. Using a tablespoon or small ice-cream scoop, portion about 2 tablespoons of batter and shape into a smooth ball (about 1.5 inches in diameter). If making ring donuts, you can pipe batter into hot oil through a pastry bag fitted with a large round tip, or drop batter and use a skewer to make a hole before frying.

Shape filled donuts

For filled rice donuts: take about 1 1/2 tablespoons of batter, flatten it in your palm into a small disc, place one portion (≈1 tbsp) of filling in the center, then fold and seal into a tight ball so the filling is enclosed. Wet your fingers if needed to help seal.

Fry donuts

Gently slide 4–6 donuts (do not overcrowd) into the hot oil. Fry, turning occasionally with a slotted spoon, until golden brown on all sides, about 3–4 minutes per batch depending on size. Filled donuts may take an extra 1–2 minutes to cook through — aim for an internal temperature that feels hot and the donut is puffed. Adjust heat as necessary to maintain 325–350°F so they cook through without burning.

Drain

Using a slotted spoon, transfer cooked donuts to a wire rack set over a baking sheet or to paper towels to drain briefly for 1–2 minutes. For a crisper finish, drain on a rack so they don't steam on the paper.

Finishing

Sugar coating

While still slightly warm, toss the donuts in powdered sugar or granulated sugar mixed with 1 tsp ground cinnamon (optional) until evenly coated. For a lighter dusting, use a fine sieve to dust powdered sugar over the donuts.

Garnish

If desired, sprinkle toasted sesame seeds or crushed roasted peanuts on top while the glaze/sugar is still tacky so they adhere. Let donuts cool 5 minutes before serving so the interior sets but serve warm for best texture.