Preheat your oven to 170°C (338°F) using both top and bottom heat. Allow it to preheat for a full 10 minutes. Grease a muffin tin or line it with paper liners.

In a large mixing bowl, combine the 80g of beaten egg, 60g of corn oil, 125g of whole milk, and 50g of fine granulated sugar. Use a whisk to stir vigorously until the mixture is smooth and the sugar has begun to dissolve.

Sift the 130g of cake flour, 20g of cornstarch, 30g of milk powder, and 8g of baking powder directly into the bowl with the wet ingredients.

Using a whisk, gently fold the dry ingredients into the wet ingredients. Mix only until no dry streaks of flour remain and the batter is smooth. Be careful not to overmix. Transfer the finished batter to a piping bag.

In a separate small bowl, combine the 10g of cold, cubed butter, 10g of powdered sugar, and 20g of cake flour. Use your fingertips to quickly rub the ingredients together until the mixture resembles coarse, sandy crumbs. Set aside.

Pipe the batter into the prepared muffin cups, filling each one only halfway. Place 3-4 fresh blueberries into the batter in each cup.

Continue to pipe more batter on top until each muffin cup is about 80% full. Place another 3-4 blueberries on top of the batter in each cup.

Generously sprinkle the prepared streusel topping over the surface of each muffin.

Immediately place the muffin tin on the middle rack of the preheated oven. Bake at 170°C (338°F) for approximately 30 minutes, or until the tops are golden brown, spring back lightly when touched, and a toothpick inserted into the center of a muffin comes out clean.

Once baked, remove the muffins from the oven. Let them cool in the tin for 5 minutes before carefully transferring them to a wire rack to cool completely. Enjoy them warm for the ultimate burst of blueberry flavor!