Combine the chopped mango, lime juice, and powdered sugar (start with 1 tbsp and add more if needed) in a blender or food processor. Blend until completely smooth. Taste and adjust sweetness if necessary. Set aside.

Place the graham cracker or digestive biscuit crumbs into a small bowl. If you don't have pre-made crumbs, crush whole biscuits in a zip-top bag using a rolling pin until fine.

In a large, chilled mixing bowl, combine the very cold heavy cream, 1/4 cup powdered sugar, and vanilla extract. Beat with an electric mixer on medium-high speed until medium-stiff peaks form. Be careful not to overbeat, or it will turn grainy.

Divide the graham cracker crumbs evenly among 4-6 small serving cups or glasses, pressing lightly into the bottom to form a base (about 1-2 tablespoons per cup).

Spoon about 1/4 to 1/3 cup of the mango puree over the crumb layer in each cup, spreading it gently.

Carefully spoon or pipe a generous layer of the whipped cream mixture over the mango puree. You can use a piping bag for a neater look, or simply spoon it in.

Repeat the layers once more if your cups are deep enough, or simply finish with the whipped cream layer.

Cover the assembled dessert cups with plastic wrap and refrigerate for at least 30 minutes (or up to 4 hours) to allow the flavors to meld and the dessert to chill thoroughly.

Before serving, garnish each cup with a fresh mint sprig and/or a small sprinkle of diced fresh mango, if desired. Serve chilled.