Set your oven’s broil to low or preheat between 450-500F. In a microwave-safe bowl, melt the chocolate in 30-second intervals, stirring in between, until fully melted. Pour the chocolate into a seasoned cast iron skillet.
Whisk in the milk or heavy cream until a smooth, homogenous ganache forms, about 1-3 minutes.
Scatter the marshmallows all over the chocolate ganache and broil for 1-2 minutes, or until the marshmallows reach a deep golden brown. Serve immediately with graham crackers, pretzels, fresh fruit, or other family favorites.