Prepare an ice water bath in a large bowl.
For the chocolate syrup combine the cocoa powder, brewed coffee, and ½ cup granulated sugar, in a small saucepan. Bring to a boil and cook for 30 seconds. Remove from the heat and add chopped bittersweet chocolate. Stir until melted. Add the vanilla and salt and set aside.
Create a slurry made with 2 tablespoons of the milk and cornstarch, whisk until smooth, set aside.
Whisk the cream cheese into the warm chocolate syrup until smooth.
In a heavy bottom 3.5 to 4 quart saucepan, combine the remaining milk, cream, sugar and corn syrup. Bring to a boil over medium-high heat and cook for 4 minutes. Off-heat whisk in the cornstarch slurry. Set the saucepan back on the heat and cook until slightly thickened, about 1 minute.
Combine the chocolate mixture with the cream mixture in a large glass or metal bowl and place in an ice water bath. Stir every 5 minutes until chilled then refrigerate overnight or at least 8 hours. Process according to your ice cream maker directions.
For the Fluffernutter:
While the ice cream is processing, whisk together the marshmallow fluff/cream, peanut butter and 2 tablespoons milk. Place the mixture in a piping bag and set aside.
Once the ice cream is frozen, layer ⅓ of the chocolate mixture in an air-tight freezer safe container. Squeeze ⅓ of the fluffernutter on top, then repeat twice more with a layer chocolate, then marshmallow, etc. Swirl the chocolate and peanut butter together using a kitchen knife or skewer. Freeze the ice cream overnight or up to 3 days.