Preheat the oven to 325°F. Line an 8-inch baking pan with parchment paper. Let about 3-4 inches of parchment paper hang over so the bars will be easy to lift out.
Put the graham crackers in a food processor and pulse until they are finely crushed. Add the brown sugar, butter, flour, and salt. Pulse until combined.
Transfer the crumb mixture into your baking pan and press the crumbs into the bottom. Bake for 12-15 minutes until crust begins to brown. Let it cool while you make the filling.
Put the cream cheese in the food processor and run until smooth. Add in the sugar and blitz again until everything is light and fluffy.
Scrape the bowl and add in the eggs one at a time while mixing
Add in the sour cream and vanilla and mix well.
Pour the batter into the cooled crust. Chop 9 of the Peanut Butter Cups, saving the rest for garnish. Gently swirl the chopped candies through the batter.
Bake until the cheesecake is just set but the middle still jiggles, about 35-40 minutes. Rotate the pan halfway through baking.
Let the pan cool on a rack for 2 hours. Cover with foil and refrigerate for 3 hours before cutting. Pull the bars from the pan and cut into squares.
Melt the semisweet chocolate in the microwave or over a double boiler and drizzle over the cooled bars. Top with the remaining chopped Peanut Butter Cups and Reese's Pieces.