1Line an 8x8 inch pan or casserole dish with parchment paper or foil. Lightly spray with non-stick cooking spray.
2Place milk chocolate chips, semi-sweet chocolate chips, and butter in a double boiler.
3Stir in sweetened condensed milk and hot chocolate mix.
4Warm double boiler over medium heat, stirring constantly until mixture has melted. If using a microwave, heat for 45 seconds, stir, and continue heating in 15 second intervals until melted.
5Once melted, stir in vanilla extract. Gently stir in 2 cups of mini marshmallows.
6Pour fudge mixture into prepared dish.
7Top with remaining mini marshmallows and gently press into fudge.