Step 1: Prep Your Equipment

Start by preheating your oven to 350°F (177°C). Prepare a 9×13 inch baking dish by lining it with parchment paper or greasing it well with non-stick spray. This step ensures the bars will lift out easily once cooled.

Step 2: Make the Crust and Crumble

In a large mixing bowl, cream the softened butter with both the granulated and brown sugars until the mixture is light and fluffy. Add baking soda and salt, mixing just until incorporated. Gradually stir in the flour and oats, blending until a crumbly, cohesive dough forms.

Take half of this mixture and press it firmly into the bottom of your prepared pan. This will be your base. Bake it in the preheated oven for about 13 minutes, or until lightly golden and set.

Step 3: Prepare the Cream Cheese Layer

While the base is baking, start on the filling. In a separate bowl, beat the cream cheese until smooth and lump-free. Gradually whisk in the sweetened condensed milk until fully incorporated and velvety in texture. Add the vanilla extract and egg yolk, mixing until everything is blended and glossy.

Step 4: Assemble the Layers

Once the crust is partially baked, remove it from the oven. Pour the cream cheese mixture over the warm crust and spread it evenly with a spatula. Evenly scatter the blueberries across the cream cheese layer, allowing their natural juices to bake right into the filling.

Sprinkle the remaining oat crumble over the top of the blueberries. Gently press down to slightly adhere the topping to the creamy layer without flattening it.

Step 5: Final Bake

Return the pan to the oven and bake for another 20 to 25 minutes. You’ll know it’s ready when the top is golden brown and slightly firm to the touch. The aroma filling your kitchen is reason enough to make this recipe again.

Step 6: Cooling and Slicing

Let the bars cool completely in the pan, ideally on a wire rack. This step is essential to prevent crumbling when you slice them. Once cool, lift them out using the parchment paper and transfer to a cutting board. Cut into neat squares or rectangles, depending on your preference.