Preheat your oven to 300°F.

Grease the wells of a 6-panel cake pan, standard 12-cup muffin tin, 9-inch deep dish pie pan or 9-inch springform pan, and set it aside.

Place the cookie/cracker crumbs in a medium-size bowl and create a well in the center. Pour in the melted butter and beaten egg, and mix to combine.

Divide the mixture evenly among the prepared wells and press into an even layer on the bottom and up the sides of the wells or the pie or springform pan.

To get a smooth bottom, try covering the bottom of a glass with plastic wrap and pressing evenly into the bottom of the wells.

Place the shells in the center of the preheated oven and bake until slightly puffed and dry to the touch (about 10 minutes—slightly less for the standard 12-cup muffin tin).

Remove from the oven and allow to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

Place the cooled shell(s) on a parchment-lined baking sheet and set aside.

Place the chocolate in a medium-size, heatproof bowl and set it aside.

Place the cream in a small, heavy-bottomed saucepan and bring to a simmer over medium-low heat.

Pour the warm cream over the chopped chocolate and allow to sit until the chocolate begins to melt.

Stir until the chocolate is melted and smooth, and then pour to divide evenly among the prepared shells or into the single shell.

Place the baking sheet in the refrigerator to set while you make the topping.

This marshmallow topping has less gelatin for a pourable consistency that still sets properly.

Bloom the gelatin in 2 fluid ounces (1/4 cup) of the cool water by placing them together in the bowl of a stand mixer fitted with the whisk attachment, or a large bowl with a hand mixer, and mix them gently to combine. The gelatin will swell as it sits.

In a small, heavy-bottom saucepan, place the remaining 2 ounces of cool water plus the sugar and cream of tartar, and stir gently to combine.

Clip a candy thermometer to the side of the saucepan, and cook over medium heat until the mixture reaches 240°F, the softball stage.

Pour the hot sugar mixture down the side of the mixer bowl of bloomed gelatin and allow to cool briefly, until no longer hot to the touch.

Add the vanilla and salt, and beat on medium speed until the marshmallow becomes thick, white and glossy (about 3 minutes). It should nearly triple in size.

Spoon or pour about 1/4 cup of the marshmallow topping in the center of the chocolate filling in each pie or as much as will comfortably fit on top of the single pie.

Spread the marshmallow topping into an even layer on top of the filling, stopping about 1-inch from the edge.

Sprinkle lightly with the optional chocolate shavings, and allow to chill in the refrigerator until set (about 30 minutes) before serving.

Keep chilled.