In a saucepan, add in the sugar, butter and milk.
On medium heat, continually stir until the mixture boils. Once it boils, continue to stir so the mixture doesn't burn.
Check the temperature with a candy thermometer and make sure that the mixture has reached 234°F/112°C. (This will take at least 5 minutes).
Once it reaches the temperature, remove it from the stove.
Immediately add in the chocolate chips and stir until everything is melted and incorporated.
Add in your marshmallow cream and stir to incorporate.
Add in vanilla (and nuts, if using) and stir.
Pour fudge mixture into your lined pan. Add sprinkles and other toppings now.
Set aside and allow to cool and set, preferably longer, before removing and cutting.