Pour the chocolate chips into a small heatproof bowl, set aside.

Add half of the heavy cream to a separate microwave-safe bowl or small saucepan and heat until steaming and just beginning to bubble around the edges (1 minute in the microwave).

Pour the hot cream over the chocolate chips and let it sit undisturbed for 1 minute to soften the chocolate. Stir slowly until the mixture is completely smooth and glossy. Set aside.

Add the remaining heavy cream, vanilla bean paste, and salt to a large mixing bowl. Using an electric mixer, beat on medium-high speed until stiff peaks form.

Reduce the mixer speed to low and beat in the sweetened condensed milk.

Using a rubber spatula, gently fold the ganache into the whipped cream until no streaks remain and the mousse is light, fluffy, and evenly combined. Be careful not to overmix, which can deflate the mousse.

Divide the mousse evenly between two serving glasses. Cover each cup with plastic wrap and refrigerate for at least 4 hours. For the best texture, chill overnight.

Once the mousse has set, spoon or spread marshmallow fluff over the top of each cup (or just sprinkle with mini marshmallows). You can toast the marshmallow fluff with a kitchen torch until golden brown or leave as is.

Serve with graham cracker pieces for dipping, scooping, or crumbling on top.