Grease a 8-inch square pan with cooking spray and set aside.
In a saucepan mix together the sweetened condensed milk and chocolate chips. Heat over low until melted, stirring constantly. Once smooth, remove from heat. Stir in the vanilla extract Let sit 5 minutes. Fold in the marshmallows and raisins, making sure not to over stir, otherwise the marshmallows will melt.
Pour the mixture into the prepared pan and smooth. Chill in the fridge until set, about 2 hours. Cut into squares and serve.
Notes
Add 1/2 cup chopped walnuts to make this into rocky road fudge.
The marshmallows will melt if you stir them too much.