Preheat the oven to 350ºF. Line an 8-inch square baking pan with parchment paper, and grease with nonstick cooking spray.

In the bowl of a stand mixer fitted with a paddle attachment, beat the sugar and lemon zest together. Add the butter, and continue beating on high until creamy. Add the vanilla, almond extract and salt, and continue beating until blended. Slowly mix in the flour.

Press dough into the bottom of the prepared pan and bake for 15-18 minutes, or until lightly browned around the edges.

While crust is baking, prepare the filling. Place blueberries into a medium saucepan over medium heat. Use a potato masher or fork to crush the berries as they soften. Once all the berries have been crushed, continue cooking until the mixture is smooth. Pour mixture through a fine mesh strainer set over a bowl, pushing out as much juice as possible. Discard the berry solids, and measure out 1/2 cup blueberry juice.

Reduce oven temperature to 325ºF, and bake for 20-24 minutes, or until the center is set. Place pan onto a wire rack to cool completely, about 2 hours. Once cool, cover bars and chill in the refrigerator for 2 more hours.

Using a sharp knife dipped in hot water and wiped dry, cut blueberry bars into squares. Dust with powdered sugar just before serving.