Prepare the Brownie Mix - Preheat the oven to 350°F (175°C). Grease a 9x13 inch baking dish. In a mixing bowl, combine the brownie mix, eggs, vegetable oil, and water. Stir until well combined and a smooth batter forms. Be sure to read the instructions on the brownie mix box to determine the exact quantities of eggs, oil, and water needed.

Bake the Brownie Layer - Pour the brownie batter into the prepared baking dish and spread it out evenly. Bake for 20-25 minutes or until a toothpick inserted into the center comes out clean. Let the brownie layer cool completely before proceeding. Don't overbake the brownie layer or it will become dry and crumbly. It's better to underbake slightly than to overbake.

Make the Cheesecake Layer - In a mixing bowl, beat the cream cheese until smooth. Add the sugar and vanilla extract and beat until well combined. Add the eggs one at a time, beating well after each addition. Be sure to use room temperature cream cheese for best results. This will ensure that the cheesecake layer is smooth and creamy.

Chop the Thin Mint Cookies - Using a knife or a food processor, finely chop the Thin Mint cookies. For a finer texture, use a food processor. For a chunkier texture, chop the cookies by hand with a knife.

Assemble the Bars - Spread the cheesecake mixture evenly over the cooled brownie layer. Sprinkle the chopped Thin Mint cookies over the top of the cheesecake layer. Bake for 25-30 minutes or until the cheesecake layer is set. Let the bars cool completely before slicing and serving. To make the bars easier to slice, chill them in the refrigerator for 1-2 hours before cutting.