Dessert

Line an 8-inch-square baking pan with wax paper or foil and coat with non-stick spray
Combine dark chocolate chips, heavy cream, and half the condensed milk in a microwave-safe bowl
Microwave the mixture in 20-second intervals, stirring between intervals, until the chocolate is melted
Add vanilla extract to the chocolate mixture and stir until smooth
Transfer the chocolate mixture to the prepared pan and spread into an even layer
Combine white chocolate chips and the remaining condensed milk in a separate microwave-safe bowl
Microwave the white chocolate mixture in 20-second intervals, stirring between intervals, until melted
Spread the white chocolate mixture evenly over the dark chocolate layer
Top the layers with miniature marshmallows and gently press them down
Refrigerate until set, about 4 hours
Remove the fudge from the pan and peel off the wax paper
Cut the fudge into bite-sized pieces and serve