In a mixing bowl, whisk together 2 eggs, 160g whole milk, and 90g granulated sugar until the sugar dissolves completely.

Gradually add 90g corn oil in two batches, whisking well after each addition until the mixture is fully emulsified and no oil streaks remain. Stir in one direction to avoid deflation.

Sift 240g cake flour and 9g baking powder together. Add this dry mixture into the wet ingredients. Use a spatula to gently fold until just combined. Avoid overmixing to prevent gluten formation. When no dry flour remains, whisk until the batter is smooth and lump-free.

In a small bowl, combine 20g cake flour, 10g powdered sugar, and 10g butter. Use your fingers to rub the butter into the dry ingredients until the mixture resembles coarse crumbs.

Transfer the prepared batter into a piping bag. Line a muffin tray with cupcake liners and pipe batter to fill each mold halfway.

Place 3 blueberries evenly on top of the batter in each mold. Adjust the quantity as desired, but avoid overcrowding to ensure proper rising.

Pipe the remaining batter on top, filling the molds and completely covering the blueberries. Place 3 more blueberries on the surface for decoration.

Sprinkle the crumb topping evenly over the surface of each muffin.

Preheat your oven to 170°C (340°F) with top and bottom heat.

Place the muffin tray on the lower rack and bake for approximately 25 minutes. If the surface browns too quickly, cover the muffins with aluminum foil to prevent overbaking.

Check for doneness by inserting a toothpick into the center of a muffin. If it comes out clean, the muffins are ready.