3cups(300g) blueberriesfresh or frozen; if using frozen, do not thaw
Preheat the oven to 350ºF (177ºC). Line an 8″ x 8″ baking pan with foil. Leave an overhang on the sides. Set aside.
Stir the melted butter, granulated sugar, vanilla extract, salt, and half of the lemon zest together in a medium bowl. Add the flour and stir until combined.
Reserve ¾ cup of the shortbread crust and place in the refrigerator or freezer until needed.
Press remaining crust evenly into the prepared pan. Bake for 18 minutes while you prepare the filling.
In the bowl of a stand mixer fitted with the paddle attachment, or in a medium sized bowl with a hand mixer, beat cream cheese on high until smooth. Beat in eggs, scraping down the sides as necessary. Add sugar, yogurt, remaining lemon zest, lemon juice, and salt and beat again. Add flour and beat one more time until just combined. Gently fold in blueberries with a spoon or spatula.
Pour filling into prepared crust and add a few blueberries on top of filling. Remove reserved crust from refrigerator and crumble over top of the filling (you may need to separate into crumbs with a knife or fork). Sprinkle with coarse sugar, if desired.
Bake bars for 55-60 minutes minutes, or until a toothpick inserted in center comes out mostly clean. Allow bars to cool at room temperature on a wire rack. When completely cool, chill in the refrigerator for 1 hour.
When bars are completely chilled, lift out of the pan using foil overhang and cut into squares. Top with lemon zest before serving, if desired. Bars can be stored covered in the refrigerator up to 5 days. Bars freeze well, up to 3 months. Thaw in the refrigerator overnight.