Indoor S'mores

Matt's friend from high school made this for a BBQ at Kristin's house last May when we were in Idaho. I just found the recipe in my planner and thought I'd share the wealth:

5 T. butter
1 pkg milk chocolate chips
2/3 cup Karo
6 cups mini marshmallows
1 tsp vanilla
8 cups Golden Grahams

Melt the butter, chocolate chips and Karo in a saucepan; add 3 cups of the marshmallows. Bring almost to a boil. Remove from heat. Add vanilla and pour over Golden Grahams. Stir in the rest of the marshmallows. Pour into greased 9x13 pan and allow to cool.