Add the softened cream cheese to a medium-sized mixing bowl and mix until it's very smooth without any lumps. Then mix in the sweetened condensed milk, tangerine zest and juice, and the vanilla. Stir until it's a creamy, smooth consistency and set aside.
Using this method to cut citrus, cut 1 dozen ¼ -inch, horizontal slices of the whole tangerines.
Place one tangerine slice in the bottom of each paper cup in the prepared muffin pan.
Evenly divide the filling among the paper cups, directly on top of the tangerine slices. Fill each one to about ¼ to ½-inch from the top.
Now place the muffin pan in the freezer for 30 minutes. (It should be firmed up, but still a bit soft.)
Evenly divide the crust on top of each cheesecake, filling it so that none of the cheese mixture is visible. Use a small, flat-bottomed spatula to very gently press down each crust, smoothing it out.
Place the pan back in the freezer, this time for about 2 hours.
To remove the cheesecakes from the pan, you can either invert it on a baking sheet, or use a small, dull knife to carefully lift each one out.
Then very slowly and gently, pull the paper cups off of each cheesecake, placing them, tangerine slice side up, on serving plates as you go. Let them sit for at least 10 minutes before serving. (They can be served frozen, semi-frozen or soft. Once they are soft, though, they don't present quite as well, and will easily fall apart as one cuts into it with their fork. My preference is when they've been defrosting for about 15 minutes -- semi-frozen. Delicious!)