Preheat the oven to 350°F. Lightly spray four 4-inch tart pans with nonstick cooking spray and set the pans on a small rimmed baking sheet.
Place the Oreo cookies in a food processor and pulse until finely ground. Add the melted butter and pulse until the cookies are moistened. Divide the mixture between the tart pans, firmly pressing into the bottom and up the sides of the pans. Bake for 5 minutes, or until fragrant and firmed, then let cool completely.
For the chocolate layer:
Combine the chocolate, cream, corn syrup, and vanilla in a large glass measuring cup or small microwave-safe bowl. Microwave for 1 1/2 minutes then stir until the chocolate melts into the cream and the mixture becomes smooth and dark in color. Reserve a 1/4 of the chocolate mixture to the refrigerator. Divide the remaining mixture evenly between the cooled crusts, spreading across the bottom of each crust. Place the tarts in the freezer while making the peanut butter mousse.
For the peanut butter mousse:
Heat the peanut butter and 3/4 cup of the cream in a microwave-safe bowl in 20-second bursts, stirring between each burst, until the peanut butter melts. Stir in the vanilla and let cool to room temperature.
In the bowl of a mixer fitted with the whisk attachment, beat the remaining 1 cup of cream and powdered sugar on high speed until thickened but not yet forming peaks. Gradually fold the cream into the cooled peanut butter mixture until no more streaks remain. Spoon the mousse over the chilled chocolate layer in each tart. Chill the tarts in the refrigerator at least 1 hour.
Remove the remaining chocolate mixture from the fridge and stir until loosened in texture. Place the chocolate mixture in a ziptop baggie and snip a small hole in one corner. Drizzle the chocolate over the tarts. Garnish with peanut butter chips. Serve or refrigerate, covered, for up to 2 days.