Step 1

Preheat oven to 400 degrees F (200 degrees C). Grease a 9x13-inch baking dish.

Step 2

Sift flour, sugar, baking powder, and salt together in a bowl. Cut 1/4 butter into flour mixture with two knives or a pastry blender until mixture resembles coarse crumbs.

Step 3

Whisk milk and egg together in a bowl; stir into flour mixture until just moistened.

Step 4

Spread blueberries in the bottom of the prepared baking dish. Sprinkle tapioca powder over blueberries; drizzle lemon juice over the top. Dot remaining butter pieces over blueberries. Drop batter in mounds over the blueberry mixture.

Step 5

Bake in the preheated oven until cobbler is golden and bubbling, about 30 minutes.