Step 1

In the bowl of a standing mixer, preferably fit with the whisk beater, beat the cream cheese, peanut butter, and sugar just until the mixture is uniform in color. Reduce the speed to low and add the vanilla. Beat in 1/4 cup of the whipped cream just until it is incorporated. With a large rubber spatula, fold in the rest of the whipped cream, mixing until the mixture is well blended but still airy.

Step 2

Scrape the mousse into the sweet peanut butter cookie tart crust and smooth the surface so that it is level. (If the dough is rolled to the exact thickness specified, the filling and ganache amounts will be exact. If the dough is rolled a little thicker, there will be a little leftover filling and ganache.) Refrigerate the tart while preparing the ganache.

Step 3

Break the milk and bittersweet chocolates into several pieces and place in the bowl of a food processor fit with the metal blade. Process until the chocolate is very finely ground.

Step 4

Bring the cream to a boil in a small saucepan over medium heat or in a heatproof glass measure in the microwave. With the food processor’s motor running, pour the hot cream through the feed tube into the chocolate mixture. Process until smooth, scraping the sides of the bowl once or twice, about 15 seconds. Add the vanilla and pulse a few times to incorporate it. Dump the ganache to a bowl. Cool to room temperature.

Step 5

Pour the ganache over the peanut butter mousse in a circular motion, being careful so that it does not land too heavily in any one spot and cause a depression in the mousse. Using a small metal spatula, start to spread the ganache to the edges of the pastry, then spread it evenly to cover the entire surface of the tart. If desired, make a spiral pattern by lightly pressing the spatula against the surface and running it from the outside of the tart to the center. Refrigerate the tart for at least 2 hours to set or up to 5 days. (You can wrap the tart well and freeze it for up to 3 months.)

Step 6

Remove the tart from the refrigerator at least 15 minutes before serving. Unmold the tart and cut it with a sharp, thin-bladed knife, dipping it in hot water after each slice. It is as good lightly chilled as it is at room temperature. Originally published January 23, 2011.