For the Crust:

1. Prepare the Oven and Pan: Preheat the oven to 350°F (175°C). Grease or line an 8×8-inch baking pan with parchment paper.

2. Make the Crust: In a medium bowl, combine the softened butter, sugar, brown sugar, baking soda, and salt. Stir until smooth and creamy.

3. Add the Dry Ingredients: Add the flour and oats to the mixture and stir until combined. The mixture will be crumbly.

4. Press the Crust: Press about 2/3 of the crust mixture into the bottom of the prepared pan. Set the remaining 1/3 aside.

For the Cream Cheese Filling:

5. Prepare the Cream Cheese Filling: In a medium bowl, beat together the softened cream cheese, sweetened condensed milk, vanilla extract, and egg yolk until smooth and creamy.

6. Pour the Cream Cheese Mixture: Pour the cream cheese mixture over the crust in the pan, spreading it evenly.

Assemble the Bars:

7. Add the Blueberries: Scatter fresh blueberries (or raspberries) over the cream cheese layer.

8. Top with Crust Crumbles: Sprinkle the remaining 1/3 of the crust mixture over the top of the blueberries and cream cheese layer.

Bake the Bars:

9. Bake: Bake for 30-35 minutes, or until the top is golden and the filling is set.

10. Cool: Let the bars cool in the pan for 10-15 minutes, then transfer to a wire rack to cool completely.

Serve:

11. Cut and Serve: Once cooled, slice the bars into squares. Garnish with extra berries or powdered sugar if desired.