Heat the oven to 350°F. Line the bottom and sides of an 8x8-inch square metal baking pan with 2 sheets of parchment paper, ensuring they hang over all four sides.

Break 16 graham cracker sheets into rough pieces and place in a food processor. Add 1/4 cup granulated sugar and 1/4 teaspoon kosher salt. Process until the texture resembles sand, about 15 seconds.

Add 9 tablespoons melted unsalted butter and pulse to combine, about 8 to 10 pulses. Reserve 2/3 cup of the mixture for topping.

Transfer the remaining mixture to the baking pan and press into an even layer. Bake for 12 to 15 minutes until fragrant and darkening around the edges. Let cool slightly.

Clean the food processor. Process 16 ounces cream cheese until smooth and fluffy, about 1 to 2 minutes. Scrape down the sides.

Add 1/2 cup granulated sugar, 2 teaspoons lemon zest, 3 tablespoons lemon juice, 1 teaspoon vanilla extract, and 1/4 teaspoon kosher salt. Process until combined, about 30 seconds. Scrape down the sides.

With the motor running, add 2 large eggs one at a time, processing until just incorporated.

Gently stir 1 1/2 cups blueberries into the cream cheese mixture. Pour into the graham cracker crust and spread evenly. Scatter the remaining 1/2 cup blueberries on top. Sprinkle with the reserved crumb mixture.

Bake until the edges are set and puffed and the center is slightly jiggly, 30 to 35 minutes.

Let cool completely on a wire rack for about 2 hours. Cover and refrigerate until chilled, at least 3 hours or overnight.

Using the parchment, lift the slab out of the pan and place on a cutting board. Dust with powdered sugar if using. Cut into 9 or 12 bars.