Preheat the oven to 375 degrees F and set an oven rack in the middle position. Line an 9 x 9-inch baking dish with parchment paper (making sure you leave plenty of overhang so you can easily remove the bars) and spray the parchment paper lightly with nonstick cooking spray.
For the crust: In a medium bowl, combine the Lorna Doone shortbread cookie crumbs, melted butter, brown sugar, and salt. Press into the bottom and barely up the sides of the prepared pan. Bake the crust for 10 minutes, remove and set aside to cool. Reduce the oven temperature to 325 degrees F.
For the cheesecake batter: In a large bowl, (use a stand mixer or hand mixers) beat the completely room temperature cream cheese, sugar, and flour together on medium speed just until smooth. Add in the sour cream, vanilla, and salt. Beat at low until combined. Be careful to not overmix this batter and to keep the mixer at low even speeds. Add in the eggs, mixing just until combined after each addition. Gently fold the twix minis into the batter.
Pour the batter into the cooled crust and smooth into an even layer. Press down any twix minis that have popped above the surface. Bake for 38-43 minutes, until the center is just set and top is not shiny (the center might still be a little jiggly and that's perfect). Remove the bars from the oven and let cool at room temperature for 1 hour. After that, cover, and chill in the fridge for 4-6 hours (I always chill overnight and like that best!)
Lift the cheesecake out of the pan (using the parchment paper overhang) and using a very hot knife, slice into even bars. (I like to run the knife under very hot water, wipe it off, and then make one slice. Repeat until the cheesecake is all sliced up!) Serve with caramel and chocolate sauce as desired (directions below). You want to serve the cheesecake right out of the fridge, so store cut bars in the fridge while you make the sauces. These cheesecake bars are best 3-4 days after making.