Place the heavy cream in a large mixing bowl. Using a hand mixer fitted with the whisk attachment (or with a stand mixer), whip the cream until it begins to thicken slighlty.
Add the confectioners' sugar and vanilla. Continue to whip the cream until it holds stiff peaks.
Add half of the lemon curd to the whipped cream and fold together with a spatula.
Spread a very thin layer of the whipped cream on the bottom of an 8 X 8-inch square baking pan.
Place graham crackers in a single layer across the bottom of the pan - fitting them in like puzzle pieces.
Divide the whipped cream mixing into thirds. Dollop ⅓ of the cream on top of the graham crackers and use an offset spatula to spread it out until smooth.
Dollop a few tablespoons of the lemon curd on top and use the back of a spoon to swirl it around.
Dot the top of the lemon curd with ⅓ of the raspberries. Tear larger berries in half.
Add the next layer of graham crackers and repeat with the remaining ingredients.
For the top layer, swirl on the lemon curd then refrigerate for at least 4 hours.
Before serving, add the remaining whole raspberries on top and sprinkle with lemon zest.