Line a 9×9 square pan with tin foil and spray the sides and bottom with cooking spray.

In a large saucepan over medium heat, add in the butter, half and half, and both sugars. Stir until combined.

Continue to stir the mixture often until it comes to a boil, then let boil for 5 minutes.

Remove from heat and immediately add in the marshmallow cream and then the chocolate chips. Stir until all of the marshmallow cream is worked in and the fudge is smooth.

Pour half of the mixture into the prepared pan.

Dump the marshmallows on top of the fudge and pour the remaining fudge on top of the marshmallows. Tap the pan on the counter until the fudge touches all of the edges.

Use a skewer to swirl the fudge and marshmallows. Tap the pan to smooth out the fudge and marshmallows.

Let it cool completely before slicing.