Make the cookie brittle:
Prepare the cookie mix according to package directions, but stir half of the cornflakes into the batter. Using oiled hands, press the dough into a ⅛-inch thick layer on a baking sheet. Scatter the remaining cornflakes over the top. Bake at 350°F until golden and crisp, about 17 minutes. Cool completely, then break into a mix of large and small chunks.
Whip the cream:
While the brittle bakes, combine heavy cream, confectioners’ sugar, peanut butter, vanilla, and salt in a mixing bowl. Whip until medium peaks form, 2 to 2 ½ minutes. Chill until ready to use.
Assemble the parfaits:
In medium glasses, layer cookie brittle, whipped cream, mango, and raspberries. Repeat with another layer of cream, brittle, fruit, and more cream. Top with a large shard of brittle and a mint leaf for garnish.
Tip:
The brittle softens as it sits. For a softer, more pudding-like parfait, cover and refrigerate overnight (up to 24 hours).
