Position oven rack to the middle position of the oven and preheat the oven to 350 degrees F.
Prepare the crust: process all crust ingredients in the bowl of a food processor fitted with the metal blade until it resembles wet sand. If you don’t have a food processor, you can combine graham cracker crumbs, coconut oil, maple syrup and salt in a large bowl. Transfer mixture to a 9-inch pie plate and press crumbs firmly into the bottom and up the sides of the dish making an even layer. The crust should be about ¼-inch thick. You can use the bottom of a cup to do this. The better you press the crust, the better it will hold together.
Bake for 10 minutes, until just slightly browned. Remove from the oven and let the crust cool if you have time. This can be done a day in advance.
To make the ice cream base: pour heavy cream, sweetened condensed milk, and vanilla extract or seeds into the bowl of a stand mixer fitted with the whisk attachment. Whisk on medium-high speed, until mixture thickens like whipped cream, about 5-8 minutes. You can use a handheld mixer if you don’t have a stand mixer. Transfer whipped mixture to cooled crust and refrigerate overnight. If you are using store-bought ice cream, soften it up a little and scoop it into the graham cracker crust. Don’t put the whole thing in one block. It will be difficult to spread out. Freeze overnight.
Position oven rack 6 inches from the broiler heat source. Set oven to broil (set to HI if there’s an option).
Top ice cream layer with marshmallow topping. You can also drizzle with chocolate sauce and then top with marshmallow creme. Place cake in the oven and broil until top is golden brown. DON’T WALK AWAY. It’s only going to take a few seconds. OR you can use a torch for this step. Remove from the oven and serve immediately or store in the freezer until ready to serve.