Whisk together the graham cracker crumbs and granulated sugar. Pour in the melted butter and mix until combined.
Press the mixture into your pan and bake for 10 minutes at 350F. You can use an 8 or 9 inch springform pan, or a regular pie pan.
Whisk together the key lime zest, lime juice, yogurt and sweetened condensed milk until smooth. Pour the filling on your pre-baked crust and bake for an additional 10 minutes.
Whisk the egg whites, sugar, cream of tartar and vanilla in a bowl over 2 inches of boiling water until thin and frothy on top. Remove from the heat and beat on high speed for 5-6 minutes until stiff peaks form.
Once the pie is cool, top with the meringue and toast it with a lighter/kitchen torch. This isn't necessary, but definitely recommended. Enjoy!