Preheat oven to 375 degrees F.
Make the chocolate tart dough. Combine all-purpose flour with cocoa powder, powdered sugar, salt, with butter in a food processor or in a large bowl. Mix until the butter is incorporated and the mixture resembles coarse sand. Add 1 egg yolk and heavy cream and mix just until the dough comes together. Shape the dough into a disc and wrap it in plastic wrap. Chill in the fridge for at least 30 minutes or until firm.
Remove the dough from the fridge and roll until it's ¼-inch thick. Place the dough into a tart pan, pressing down the dough onto the pan. Place a parchment paper on top with baking weights such as beans or rice. Bake the tart for 20 minutes. Remove the weights and paper and continue to bake for another 10 minutes. Remove from the oven and cool completely.
Meanwhile, make the caramel. Heat granulated sugar in a heavy-bottomed pot over medium-low heat. Melt the sugar until it starts to become amber brown. Add the heavy cream and bring to a boil for 1 minute. Remove from heat and stir in butter and sea salt, stirring until the butter has melted. Add chopped peanuts and let cool slightly.
Pour the peanut caramel into the chocolate tart. Let cool.
Make the peanut butter mousse. Whip heavy cream until stiff peaks form. Beat together peanut butter with powdered sugar, and cream cheese until smooth. Add vanilla and beat until smooth. Add ⅓ of the whipped cream and mix until incorporated. Fold in the remaining whipped cream until smooth.
Spread the peanut butter mousse on top of the caramel in the tart. Chill the tart in the fridge for at least 1 hour or overnight.
Melt semisweet chocolate with heavy cream in the microwave for 30 seconds. Stir to combine and continue to microwave at 20 second intervals until the chocolate has melted, stirring well each time.
Spread the chocolate ganache on top. Let rest for 30 minutes or until the chocolate sets. Serve.