Key Lime Pie

14 ounces sweetened condensed milk
1/2 cup key lime juice
1 teaspoon grated lime zest
3 large eggs -- separated
8 pre-baked pie crust -- or graham cracker crust
1/4 teaspoon cream of tartar
1/4 cup sugar

Preheat oven to 325°. In a medium bowl, combine the milk, lime juice, and zest; blend in the egg yolks. Pour the filling into the crust. For the meringue, beat the egg whites with the cream of tartar until soft peaks form. Gradually beat in the sugar until the mixture has stiff peaks. Spread the meringue over the filling; spread it to ouch the edge of the crust all around. Bake for 12-15 minutes, or until the meringue is golden brown.