Before starting anything, throw a metal or glass mixing bowl and the beaters for your hand mixer into the freezer.
Preheat your grill to 325°F, if you find your grill runs hot; use the rear burner instead of one bottom burner. Prepare for indirect grilling.
Combine the melted butter and crushed cookie. Press the mixture evenly into the bottom and up the sides of a tart pan with a removable bottom. You can use a circle or rectangular one. Bake over indirect heat for 10 minutes, then remove to cool. Turn off the grill.
Turn your side burner on to low. To melt the chocolate, place the bottom pot of a double boiler, half filled with water, on to the side burner and allow it to come to a gentle simmer. Add the chopped chocolate to the top half of a double boiler, or to a heatproof bowl whose bottom fits into the mouth of the simmering pot without submerging in the water.
Gently melt the chocolate, using a spatula to move the chocolate around. While the chocolate is melting, combine ¼ cup of whipping cream and espresso powder. Gently warm in the microwave for 30 to 40 seconds, just so it’s not cold, but not boiling either. Once all of the chocolate is melted, remove the chocolate and water from the heat together and stir in the coconut oil, and cream mixture.
Pour the chocolate mixture into the waiting tart crust and chill for at least 2 hours.
For the Stabilized Whipped Cream: When you are ready to serve, or when the tart has set, make the stabilized whipped cream. Remove the bowl and beaters from the freezer and pour in 1 cup of cream. Begin mixing on high speed until soft peaks form. This means that the whipped cream has whipped enough to mostly stay put if you touch it, but all the ridges are soft.
Place 2 tbsp. of marshmallow fluff, or 3 regular sized marshmallows into a bowl and warm for 15 to 20 seconds. Add the marshmallows to the whipping cream and continue beating at medium-high speed until stiff peaks form and all of the marshmallow has been incorporated. Scoop the whipped cream into a piping bag with a tip and pipe it on to the tart. Garnish with chocolate covered espresso beans.
Serve immediately after piping the whipped cream, or chill for later. The whipped cream is stabilized and will stay put for a few days. Just remember to use a knife warmed under hot water for easy slicing.