1

Preheat oven to 325°F degrees. Lightly coat side and bottom of a 9 1/2-inch fluted tart pan (with removable bottom) with cooking spray. In a small bowl, combine graham cracker crumbs, melted butter and a pinch salt. Gently press crumb mixture into bottom of pan in an even layer (use the back of a spoon to flatten). Bake 5 minutes.

2

While crust bakes, beat together cream cheese, yogurt, 1 c sugar, eggs, Key lime juice and zest until smooth. Evenly pour mixture over crust; bake until set on top, about 30 minutes. Let cake cool completely, about 1 hour. (Cake can be made up to one day ahead. Cover and refrigerate.)

3

While cake cools, place egg white, 1/4 c sugar and cream of tartar in heatproof bowl of electric stand mixer; set over a saucepan of simmering water. Whisk by hand constantly until sugar is dissolved and whites are warm to the touch, about 2 minutes. Remove bowl from heat; beat with electric mixer fitted with whisk attachment, starting on low speed, gradually increasing to high, until stiff, glossy peaks form, 5-7 minutes. Add vanilla and pinch salt; mix until combined. (Frosting can be made up to one day ahead. Cover and refrigerate.)

4

Decorate top of cooled cake with frosting; use a torch to brown frosting, if desired. Sprinkle cake with lime zest, if using; slice into 12 pieces and serve.