If using fresh soursop, cut the fruit in half and scoop out the white pulp into a bowl. Remove all black seeds and any fibrous parts. If using frozen pulp, thaw completely and drain excess liquid. You should have about 2 cups of clean pulp.

Place the soursop pulp in a blender or food processor. Add the sweetened condensed milk and blend on medium speed until smooth and well combined, about 1-2 minutes. The mixture should be creamy with no large chunks remaining.

In a large mixing bowl, pour the heavy cream. Using a hand mixer or stand mixer with whisk attachment, beat the cream on medium-high speed until soft peaks form, about 3-4 minutes. Be careful not to overwhip.

Gently fold the soursop mixture into the whipped cream using a rubber spatula. Use a folding motion from bottom to top to maintain the airiness. Continue until no white streaks remain and the mixture is uniform in color.

Taste and add sugar if desired, folding gently to incorporate. Add vanilla extract and a pinch of salt to enhance flavors, folding once more.

Divide the mousse among 6 serving glasses or bowls. Cover each with plastic wrap, ensuring the wrap touches the surface to prevent a skin from forming.

Refrigerate for at least 3 hours or until well chilled and set. The esponjado will firm up slightly but maintain its light, airy texture.

Before serving, garnish with a small mint leaf or a sprinkle of cinnamon if desired. Serve cold directly from the refrigerator.