How to Make It
Heat oven to 350°F. Line an 8-inch square baking pan with 2 crisscrossed pieces of parchment, leaving an overhang on all sides.
Combine the brown sugar, flour, baking powder, cinnamon, salt, and oats in a large bowl. Stir in the melted butter and mix until the pieces form a coarse crumble. Spoon 2 cups of the mixture into the bottom of the pan and gently press into an even layer; reserve the rest.
Combine the maple syrup, yogurt and cornstarch in another bowl. Pour into the pan and spread into an even layer. Scatter with blueberries and top with remaining crumble.
Bake for 45 minutes, until light golden brown. Remove from oven and let rest for 30 minutes, then transfer to the refrigerator to cool for 1 hour more. Slice into bars and serve. Bars will keep, refrigerated in an airtight container, for 3 days.