
Preheat oven to 375°F (190°C). Line an 8-inch square baking pan with parchment paper.
In a large bowl, mix oats, flour, brown sugar, baking soda, salt, and cinnamon.
Stir in melted butter and vanilla extract until crumbly.
Press half of the oat mixture firmly into the pan to form the base.
In another bowl, toss blueberries with sugar and cornstarch. Spread over the oat base.
Crumble the remaining oat mixture on top, gently pressing down.
Bake for 35-40 minutes, until golden brown and the blueberries are bubbly.
Cool completely, then lift out using parchment paper and cut into squares.