To make the crust: Preheat the oven to 350 degrees F. In a food processor, pulse together the cereal, butter and brown sugar until crumbly. Pack about 1/4 cup of the crust mixture into each of six 5-inch mini pie plates and place on a baking sheet. Bake until the crusts are lightly toasted, about 10 minutes.
To make the filling: While the crusts bake, whisk together the condensed milk, sour cream, lime zest and lime juice in a bowl. As soon as the crusts come out of the oven, carefully pour in the filling (about 1/2 cup in each) and place them back in the oven. Bake until the filling starts to set, about 10 minutes. Carefully remove the pies from the oven and let cool to room temperature, then refrigerate until chilled all the way through, at least 1 hour, though overnight is best.
To make the whipped cream: Combine the heavy cream, confectioners? sugar, vanilla and lime zest in a bowl and beat with a whisk or an electric mixer until the heavy cream forms soft peaks when the whisk is lifted out of the bowl, about 4 minutes. (Or use a stand mixer with the whisk attachment?this will make things go much faster, so watch it carefully.) Spoon the whipped cream on top of the pies and top with more lime zest.