How to Make It
Preheat the oven to 350°. In a food processor, pulse the graham cracker crumbs with the melted butter and light brown sugar until the crumbs are moistened. Press the crumbs evenly into a 9-inch glass or metal pie plate. Bake for about 10 minutes, just until lightly browned. Let cool. Increase the oven temperature to 425°.
Scrape the condensed milk into a 9-by-13-inch glass baking dish and sprinkle with a scant 1/2 teaspoon of fleur de sel. Cover the dish with foil and place it in a roasting pan. Add enough hot water to the pan to reach one-third of the way up the side of the baking dish. Bake, lifting the foil to stir 2 or 3 times, until the condensed milk is golden and thickened, about 2 hours; add more water to the roasting pan as necessary. The consistency of the caramel should be like dulce de leche. Don't worry if it is lumpy; it will smooth out as it chills.
Scrape the caramel filling into the pie crust, smoothing the top. Spray a sheet of plastic wrap with vegetable oil spray and cover the pie. Refrigerate until the filling is chilled and set, at least 4 hours.
In a bowl, using an electric mixer, beat the cream with the confectioners' sugar until firm. Remove the plastic. Mound the whipped cream on top of the pie and sprinkle with fleur de sel. Cut into wedges and serve.