Add one 8-ounce package of cream cheese and 1/4 cup of butter into a stand mixer or large mixing bowl, to soften. Set aside.
Make the pudding.* Add two (4.3-ounce) boxes of cook-and-serve lemon pudding to a 3 quart saucepan. Add 1 and 1/2 cups granulated sugar and whisk together. Add 6 egg yolks. Add 5 and 1/4 cups whole milk. Whisk it all together thoroughly, making sure there are no lumps or bits of egg. Put your back into it, now. Set the pan over medium heat and use the whisk to stir frequently for the first couple of minutes. After about 2 minutes, stick around and whisk constantly. We don't want any lumps in our pudding and this is where the magic happens, so don't walk away! You need to whisk until the mixture starts to boil. As soon as you see bubbles coming up from the bottom of the pan, turn off the burner and remove from heat.
Once the pudding has cooled for a couple minutes (Keep whisking every now and then), press plastic wrap directly on top of the pudding and up the sides of the pot (a film will form on top of your pudding if you don't.) Chill in the fridge while you make the rest. Pudding will thicken as is cools.
Meanwhile, make the crust. Preheat the oven to 350 degrees F. Add the whole 15.25-ounce package of Lemon Oreos to a food processor (about 29 Oreos.) Add 1 and 1/2 cups pecans and 1/4 teaspoon kosher salt. Process until the Oreos and pecans have turned into fine crumbs, stopping to stir as necessary. Add the melted butter and pulse to combine.
Scrape the mixture into a glass 9x13 inch casserole dish. Use your hands or a measuring cup to press the crust firmly into the pan. Bake at 350 for about 20-25 minutes, until lightly browned on top. Set aside to let cool. Make the cream cheese layer. Beat the softened 8 ounces of cream cheese and 1/4 cup butter that you already have in a bowl. Beat until it is smooth and there are no lumps, scraping the sides of the bowl with a spatula as necessary.
Add 1 and 1/2 cups powdered sugar and 1/4 teaspoon salt. Beat well.
Add the zest from one lemon, use a microplane grater if you value your sanity. Add 2 tablespoons lemon juice, or more if you're feeling frisky. Beat well. Once the crust is cool enough to comfortably put your hand on it for several seconds, add the cream cheese layer. Spread it all the way to the edges of the pan so you don't have any mixing of layers.
Top with the lemon pudding that should be not-hot and a little more set up at this point. Spread all the way to the edges.
Use another sheet of plastic wrap to cover the pudding layer, pressing it right onto the pudding so it doesn't make a film. Try to get any big bubbles out from under the plastic. Chill these layers for at least 3-4 hours, or overnight is great too.
Make the whipped cream. Just before you are ready to serve, make the whipped cream. In a large bowl or stand mixer, beat cold heavy cream on high speed. Add 1/2 cup powdered sugar, 1/4 teaspoon kosher salt, and 1 teaspoon of vanilla extract or lemon juice. Beat until soft peaks form.
Spread the whipped cream over the top of the lemon pudding layer. Chill until ready to serve. It's best not to cover at this point, so you don't ruin the pretty whipped cream on top.
Use a sharp knife to make slices, cleaning the knife each time. Sprinkle each serving with lemon zest, or toasted crushed pecans, or more crushed lemon oreos if you want!
To make the lemon twisties you see in the photos, slice a lemon into thin rounds, then make a slice halfway through the center of each round. Arrange on top of the Lemon Lush just before serving.