1. Line an 8×8 baking pan with aluminum foil or parchment paper, leaving a bit of overhang on the sides to pull out easily for slicing and serving.
2. In a large mixing bowl, combine the Oreo crumbs with the melted butter and granulated sugar, stirring to combine. Press the crumbs down firmly into the pan, using the back of a spoon or measuring cup. Place the pan in the fridge or freezer while you prepare the filling.
3. In the bowl of a stand mixer fitted with the paddle attachment, or using a handheld electric mixer, whip the cream cheese and powdered sugar together on high until light and fluffy, about 2 minutes. Add the vanilla extract and Greek yogurt, and whip again for another minute or two.
4. In another bowl using a handheld electric mixer, or in a clean mixing bowl using your stand mixer fitted with the whisk attachment, whip the heavy cream on high until stiff peaks form. Fold the whipping cream into the cream cheese mixture using a spatula, until combined.
5. Remove the pan from the freezer or fridge, and empty the filling into the crust, smoothing it all out with a spatula. Place the entire pan into the fridge for 4-6 hours until firm. Using the overhang of aluminum foil, remove the bars from the pan onto a cutting board, and using a very sharp knife, cut the bars into even squares (9 or 16). Clean the knife before each cut. Top with desired topping, or serve plain.

Leftovers may be kept in an airtight container, for 3-4 days in the fridge, or in the freezer (before topping) for up to 2 months. Thaw overnight in the fridge, before serving.