Preheat oven to 350.
Mix graham cracker crumbs, brown sugar, and a pinch of salt.
Add melted butter and form a crust in a 10 inch metal pie tin.
Bake for 10 min; let cool completely.
In a bowl, whisk egg yolks, sweetened condensed milk, key lime juice, and another pinch of salt until smooth.
Pour filling into cooled crust; put in the oven.
Lower oven temperature to 325 and bake 20-25 minutes or until the edges are set and slightly jiggly in the center.
Cool to room temperature.
Refrigerate until firm; at least 6 hours.
Serve with whipped cream and fresh limes.