Use a food processor or place the crackers in a plastic bag and crush them with a rolling pin until they’re fine crumbs.
Combine the graham cracker crumbs with melted butter and a bit of sugar if desired. Mix until the crumbs are evenly coated and resemble wet sand.
Spoon the mixture into tartlet pans or muffin tins. Press the crumbs firmly into the bottom and up the sides to form a crust. Use the back of a spoon or your fingers to ensure they’re well-packed.
Preheat your oven to 350°F (175°C).
Place the tartlet pans in the oven and bake for about 8-10 minutes, or until the crusts are golden brown. Allow them to cool completely before adding the filling.
In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer. Do not let it boil.
Place the chocolate chips in a heatproof bowl. Pour the hot cream over the chocolate chips and let sit for 1-2 minutes. Stir until smooth and fully combined, creating a rich chocolate ganache.
Spoon the chocolate ganache into the cooled tartlet crusts, smoothing it out with the back of a spoon or a spatula.
Arrange mini marshmallows on top of the chocolate filling. You can pack them closely or spread them out for a more even toasting.
Place the tartlets under the broiler on a top rack, keeping a close eye on them. Broil for 1-2 minutes, or until the marshmallows are golden brown and slightly toasted. Watch carefully to prevent burning.
Allow the tartlets to cool slightly before serving. This lets the chocolate filling set a bit more and makes them easier to handle.