Preheat the oven to 350°F and position a rack in the lower third.

Sift the cake flour with 3/4 cup granulated sugar into a bowl and set aside.

In a large mixing bowl, beat the egg whites with the cream of tartar and salt on medium speed until frothy.

Add the vanilla extract and key lime zest, then gradually add the remaining 3/4 cup granulated sugar, beating until stiff, glossy peaks form.

Gently fold the dry flour mixture into the meringue in three additions, taking care not to deflate the whites.

Fold in 2 tablespoons of the key lime juice, then pour the batter into an ungreased 10-inch tube pan and smooth the top.

Bake for 35 to 40 minutes, or until the cake is golden and springs back when lightly touched.

Immediately invert the pan on a bottle or funnel and let the cake cool completely, about 1 hour.

Meanwhile, whisk the confectioners’ sugar with the milk and remaining 2 tablespoons of key lime juice until smooth to make the glaze.

Run a thin knife around the pan to release the cake, transfer it to a serving plate, and drizzle the glaze over the top.