First, preheat your oven to 350°F. Prepare your pan by lining it with parchment paper or lightly spraying with cooking spray. In a large bowl, combine butter, sugar, baking soda, salt, flour, and oats until crumbly. Press half of the mixture into the pan for the base and bake for 13 minutes.
While the crust bakes, beat the cream cheese until smooth. Gradually add sweetened condensed milk, then whisk in eggs and vanilla until fully combined. Ensure your cream cheese is at room temperature for a silky texture.
Pour the filling over the pre-baked crust and spread evenly. Sprinkle blueberries on top, then crumble the remaining oat mixture over the berries. Gently press the crumble into the filling.
Bake for 20-25 minutes until the edges turn golden brown. Let the bars cool completely, then refrigerate before cutting to allow the filling to set.