01 -
Preheat oven to 350°F. Line 8x8 pan with foil and grease with butter.
02 -
Mix flour, oats, sugars, cinnamon, and salt. Add melted butter and egg yolk.
03 -
Reserve 1 cup mixture. Press remainder into prepared pan.
04 -
Mix blueberries, lemon juice, sugar, and cornstarch. Spread over base.
05 -
Mix extra brown sugar into reserved mixture. Crumble over blueberries.
06 -
Bake 40-45 minutes until bubbly and golden. Cool completely (3+ hours) before cutting.