- 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 (known as "the soft ball stage") on a candy thermometer
image: http://ir-na.amazon-adsystem.com/e/ir?t=yammsnosh04-20&l=as2&o=1&a=B001FB6IFY(or you can test if it's done by putting a spoonful of the boiling mixture into a cup of ice water. If you form it into a soft ball, it's ready).
- 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.