1 (9 inch) prepared graham cracker crust
2 (14 ounce) cans sweetened condensed milk
1 (16 ounce) package frozen whipped topping, thawed
Pour the condensed milk into a heatproof bowl. Set over a pan or pot of simmering water. Cook, stirring occasionally for about 2 hours, replacing water as needed. (It is extremely important not to let the water run out!) When ready, the milk should be deep golden brown and thick.
Pour the caramelized milk into graham cracker crust and allow to cool. Top with whipped topping before serving.