Preheat oven to 350°F and line cupcake tins with cupcake liners. In a small bowl, mix together graham cracker crumbs, 3 T of sugar and 4 T of butter.
Press a scant tablespoon of the graham cracker crumb mixture into the cupcakes liners.
Boil 1 cup water in microwave. Whisk in cocoa and vinegar until smooth. Let cool.
Meanwhile, in a stand mixer, beat 1 stick butter for 4 to 5 minutes on high speed. Add the sugar and beat for another couple minutes. Add the oil and eggs, mixing well. Stir in the cocoa mixture.
In a separate bowl, whisk together the flour, salt and baking soda. Add to the mixer and mix until just combined. Fill lined cupcake tins about 2/3 full.
Bake for 12-15 minutes or until they spring back when lightly touched. Cool completely on wire racks.
Using a sharp knife, cut a wedge shaped piece out of the center of each cupcake. Fill with a teaspoon or two of marshmallow fluff.
To make the frosting, beat the butter until smooth. Beat in 3 cups of powdered sugar until smooth. Add enough of the milk to reach the right consistency for spreading or piping. Add salt to taste.
Frost the cupcakes and sprinkle with additional graham cracker crumbs if desired.