In a stand mixer fitted with the whisk attachment, beat the cold heavy cream, powdered sugar, and vanilla extract on medium-high speed until stiff peaks form, about 2 to 3 minutes. Transfer to a bowl and refrigerate.

Wash and dry the mixer bowl. Using the paddle attachment, beat the cream cheese on medium-high speed until smooth and fluffy, about 1 to 2 minutes.

Add the lemon pudding mix, cold milk, lemon zest, lemon juice, and kosher salt. Beat until smooth and thickened, about 2 minutes.

Gently fold half of the whipped cream, about 1¾ cups, into the cream cheese mixture using a flexible spatula until just combined.

Arrange a single layer of graham crackers in the bottom of an 8x8-inch baking dish, breaking them as needed to fit.

Spread 1 cup of the lemon filling evenly over the crackers.

Spoon ¾ cup of the blueberry pie filling evenly over the lemon layer.

Repeat the layers with graham crackers, lemon filling, and blueberry pie filling, saving the remaining blueberry pie filling for serving.

Add one final layer of graham crackers and the remaining lemon filling.

Spread the reserved whipped cream evenly over the top.

Refrigerate for at least 6 hours or overnight until fully set and the crackers have softened.

Before serving, top with fresh blueberries and extra lemon zest. Slice into 9 squares and serve chilled with the remaining blueberry pie filling on the side if desired.