How to Make It
In a bowl, dissolve the gelatin in the water and let stand for 5 minutes. In a saucepan, cook the cream over moderately high heat until it bubbles around the edge. In a medium bowl, whisk the egg yolks with the sugar. Gradually whisk the hot cream into the egg yolks. Pour the mixture into the saucepan and cook over moderately low heat, stirring constantly, until thickened, 3 minutes. Remove from the heat and whisk in the peanut butter, followed by the gelatin. Scrape the peanut butter mixture into the bottom of six 12-ounce jars or parfait glasses and refrigerate for 1 hour, until set.
In a small saucepan, heat the half-and-half until it bubbles around the edge. In a medium bowl, whisk the egg yolks with the sugar. Gradually whisk the hot half-and-half into the egg yolks. Pour the mixture into the saucepan and cook over low heat, stirring, until thickened, about 2 minutes. Place both chocolates in a medium bowl. Pour the half-and-half mixture over the chocolate and let stand for 1 minute, then whisk until completely melted.
In another medium bowl, beat the heavy cream until softly whipped. Stir one-fourth of the whipped cream into the chocolate mixture; gently fold in the remaining whipped cream. Pour the chocolate mousse over the peanut butter mousse and refrigerate for 1 hour, until set.
In a medium saucepan, cook the sugar with 1/4 cup of the water over moderately high heat until the sugar is dissolved, washing down the side of the pan with a wet pastry brush. Continue cooking, without stirring, until a honey-colored caramel forms, 7 minutes. Remove from the heat and stir in the remaining 1/4 cup plus 2 tablespoons of water. Let cool for 1 hour.
To serve, pour a thick layer of the caramel sauce over the chocolate mousse. Top with the caramel corn and serve.