Garnish: bittersweet chocolate shavings (about 1/2 ounce,
shaved with a vegetable peeler from a bar of chocolate)
Make Crust: Cook sugar in a dry small
nonstick skillet over moderate heat, undisturbed, until it
begins to melt. Continue to cook, stirring occasionally with
a fork, until sugar is melted into a deep golden caramel, 2
to 3 minutes.
Remove pan from heat, then immediately stir in cereal and
quickly transfer to springform pan, spreading evenly over
bottom and smoothing top with back of a small spoon. (If
using pie plate, press crust up side of plate slightly.)
Sprinkle chopped chocolate evenly over warm crust to
melt, then spread melted chocolate with back of spoon to
cover crust. Cool until chocolate is hardened.
Make Filling: Dissolve instant coffee in 2 tablespoons
milk in a small bowl, then stir in gelatin and let stand.
Whisk together cornstarch and remaining 1 cup milk in a 1
1/2 to 2-quart heavy saucepan and bring to a simmer over low
heat, stirring constantly (this will take about 15 minutes;
1 percent milk curdles easily if heated too quickly).
Continue to simmer, stirring, 2 minutes.
Remove from heat, then add gelatin mixture, chocolate,
brown sugar, and rum, whisking until smooth, about 1 minute.
Transfer mixture to a metal bowl set in a larger bowl of ice
and cold water. Cool filling, whisking constantly (so
gelatin doesn't set unevenly), just to room temperature, 3
to 5 minutes, then pour over crust in pan. Chill, covered,
until set, about 3 hours.
Make topping: Beat cream with brown sugar using an
electric mixer until it just holds stiff peaks. Dissolve
instant coffee in rum and fold into cream.
Spread evenly over chilled custard, then run a thin sharp
knife around edge of "pie" and remove side of pan. Garnish
with chocolate shavings.
Cooks' note: If using a pie plate, do not unmold.