Step 1

Preheat oven to 375°. Rub a 9×13 casserole dish with cold butter, rubbing it all over the bottom and up the sides.

Step 2

Wash blueberries first and let them dry a little on a towel.

Step 3

Combine blueberries with sugar, lemon, zest, and flour in a bowl. Mix it well and then spread it all evenly in the prepared baking dish.

Step 4

In a large mixing bowl, combine all dry ingredients for the oat topping and mix well, until evenly incorporated.

Step 5

Pour in melted butter all over as you are mixing the topping. Mix until completely combined and crumbly.

Step 6

Spread oat topping evenly over the blueberries.

Step 7

Bake for about 35 minutes, until topping is golden brown and blueberries bubble.