For the crust, preheat the oven to 375°. Line an 8-inch square metal pan with foil, leaving a 2-inch overhang. In a food processor, add the cookies, butter, brown sugar, and sea salt. Pulse until the cookies are finely ground. Firmly press into the bottom of the pan using a flat-bottom glass or measuring cup to smooth the top. Bake until slightly darker around the edges, 12 to 13 minutes. Let pan cool on a wire rack, about 15 minutes.