1 cup bittersweet chocolate chips, peanut butter chips, white chocolate chips, butterscotch chips, or any combination (about 6 ounces)
1 cup coarsely chopped nuts, such as pecans or almonds
1 (14-ounce) can sweetened condensed milk
Heat the oven to 350°F and arrange a rack in the middle.
Place the graham crackers in a resealable plastic bag, press out the air, and seal, leaving about 1 inch unsealed. Using a rolling pin, roll over the crackers until they are fine, uniform crumbs (you should have about 1 cup of crumbs). Alternatively, you can place the crackers in a food processor fitted with a blade attachment and process for about 1 minute.
Place the butter in a 13-by-9-inch baking dish and place in the oven until the butter has melted, about 10 minutes.
Remove the dish from the oven and tilt it so the butter evenly coats the bottom. Sprinkle the graham cracker crumbs evenly over the butter, then sprinkle the coconut over the crumbs. Sprinkle the chocolate, peanut butter, white chocolate, or butterscotch chips over the coconut, then sprinkle the nuts over the chips. Evenly drizzle the condensed milk over all of the layers.
Bake until golden brown around the edges and springy to the touch, about 20 to 30 minutes. Remove to a wire rack and cool completely. Cut into 24 squares and serve.