Start with adding ¼ cup of heavy whipping cream and the dulce de leche in a medium bowl. Mix to combine, then set aside.
In a large bowl, add 1 cup of heavy whipping cream. Whip it on medium-high speed until it becomes thick and forms stiff peaks. This should take about 5 minutes.
Now gently fold the whipped cream into the dulce de leche until there are no more white streaks left.
Put the mousse into desired glasses and serve immediately, or place it in the fridge until ready to enjoy!