Heat oven to 350F. Add the cookies to a food processor and pulse until you have fine crumbs. Drizzle in the melted butter and pulse until combined. If you don't have a processor handy you could instead use a plastic bag and rolling pin, then just mix the crumbs and butter in a large bowl
Dump the mixture into a 9" pie dish then distribute and use a flat-bottomed glass or measuring cup to press the crumbs firmly down. You can use your fingers to press the top down as the side Is compressed.
Bake crust at 350F for 10 minutes.
While the crust Is baking zest two limes and set aside then squeeze 2/3 cup of juice and strain out the seeds.
Add the egg yolks and zest to the bowl of a stand mixer fitted with a whisk attachment and beat for a minute or so.
Pour in the sweetened condensed milk and mix on medium until fully incorporated then scrape the bowl down and pour in the key lime juice while the mixer runs on low. Scrape the bowl down once more and mix.
Pour the filling into the warm crust and give it a jiggle to level things out. Bake at 350F for about 10 minutes then cool on a wire rack for about 20 minutes and chill for at least an hour. You'll see some tiny holes in the pie and it will jiggle slightly when it's done baking.
Top the pie with dollops of whipped cream and serve.
Video
Notes
Almost any cookie will work for the crust and yes you ca use Graham Crackers although the Biscoff cookies have more flavor.
Always use fresh lime juice. If you can't find key limes then use regular limes.
You can use less zest and sub in a few tablespoons of water for some of the lime juice if you want a mellower flavor.
I piped dollops on the edge of my pie but this pie is wonderful with a giant mound of whipped cream on top so go ahead and spoon it on!