Line an 8x8 inch square pan with parchment paper and grease it lightly.

Place the chocolate chips and vanilla in a large bowl. Set aside.

Combine the butter, milk, syrup, and sugar in a medium pot (it should come about half way up the sides of the pan). Cook on medium heat.

Bring the mixture to a boil, stirring constantly until it reaches 234ºF (soft ball stage) on a candy thermometer.

Remove from the heat and stir in the marshmallows or marshmallow creme until the mixture is smooth.

Pour the mixture over the chocolate chips and stir until all the chocolate is melted and the mixture is smooth. Add the nuts if using.

Pour the mixture into the prepared pan and cool completely before cutting.