Mix 1 cup graham cracker crumbs with 6 tablespoons melted butter and a pinch of salt until everything resembles damp sand. Press this mixture firmly into the bottom of a 9x13 baking dish—you'll hear it crunch as you press. I use the bottom of a measuring cup to get it super compact and even.

Whisk together 1 cup sweetened condensed milk and 1/2 cup fresh lemon juice in a bowl. The mixture will thicken up almost immediately, which is totally normal and exactly what you want. Don't panic if it looks like it's breaking apart at first—keep whisking and it'll come together into a creamy pudding.

In a separate bowl, whip 1 cup heavy whipping cream with 1/4 cup powdered sugar and 1 teaspoon vanilla extract until you get stiff peaks. This takes about 3 to 4 minutes with an electric mixer on medium-high speed. Fold this whipped cream gently into the lemon mixture until no white streaks remain.

Dissolve 2 packages of lemon gelatin in 1 cup boiling water, stirring for about 2 minutes to make sure it's completely dissolved. Let this cool for 5 minutes—you don't want it piping hot or it'll deflate your whipped cream. Then gently fold the gelatin mixture into the lemon cream until it's fully combined.

Fold 1 cup whipped topping into the lemon mixture gently and carefully. The texture should look fluffy and cloud-like at this point. Pour everything over your graham cracker crust and smooth the top with a spatula.

Cover the dish with plastic wrap and refrigerate for at least 4 hours, or overnight if you've got the time. The longer it chills, the more the flavors meld together beautifully. I always make mine the day before because it's one less thing to worry about.

Before serving, top with 1/4 cup chopped pistachios and lemon slices for a pretty presentation. Cut into 12 squares and serve straight from the fridge. This no bake lemon icebox cake stays perfectly set and tastes best when it's cold.