Preheat Oven and Prepare Pan:
Preheat the oven to 350ºF (177ºC). Line an 8″ x 8″ or 9″ x 9″ baking pan with foil, leaving an overhang on the sides for easy removal. Set aside.
Make the Shortbread Crust:
In a medium bowl, stir together the melted butter, granulated sugar, vanilla extract, salt, and lemon zest.
Add the flour and mix until fully combined.
Reserve 3/4 cup of the shortbread crust mixture and place it in the refrigerator or freezer until needed.
Press the remaining crust evenly into the prepared baking pan and bake for 18 minutes.
Prepare the Filling:
In a stand mixer fitted with the paddle attachment (or using a hand mixer), beat the cream cheese on high until smooth.
Add the granulated sugar and lemon zest and beat until creamy.
Add the eggs one at a time, beating until fully incorporated.
Add the yogurt, lemon juice, and salt, and beat again until smooth.
Finally, add the flour and mix just until combined.
Gently fold in the blueberries with a spatula.
Assemble and Bake:
Pour the filling over the pre-baked crust.
Scatter a few extra blueberries on top, then crumble the reserved shortbread crust over the filling.
Optionally, sprinkle the top with additional granulated sugar or coarse sugar.
Bake the bars for 55-60 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bars to cool at room temperature on a wire rack, then chill them in the refrigerator for at least 1 hour.
Serve:
Once chilled, lift the bars out of the pan using the foil overhang and cut them into squares.
Top with additional lemon zest, if desired. Store the bars covered in the refrigerator for up to 5 days. They can also be frozen for up to 3 months; thaw overnight in the fridge.