Line your 9x9 inch baking pan with parchment paper, leaving some overhang for easy removal later.
In a medium saucepan over medium heat, combine the butter and sugar. Stir continuously until the butter is melted and the sugar is well incorporated.
Slowly pour in the evaporated milk, stirring constantly to combine. Bring to a gentle boil, and let it boil for about 5 minutes, stirring frequently.
Remove from heat and stir in the chocolate chips and marshmallow cream. Mix until fully melted and smooth.
Stir in the vanilla extract until evenly distributed.
Pour the mixture into the prepared baking pan. Spread evenly and let cool at room temperature for about 2 hours. Refrigerate for at least 2 more hours until fully set.
