Tangerine-Vanilla Tea Cakes

For the cakes:
Preheat oven to 350u0b0F and spray two 12-cup standard muffin pans with nonstick spray. Whisk together cake flour, baking powder, baking soda, and salt in a medium bowl. Beat butter and sugar in a large mixer bowl at medium speed until fluffy. Add egg yolks, 1 at a time, and beat until combined; beat in vanilla and tangerine zest. Combine tangerine juice and buttermilk in a small bowl. Reduce speed to low and add half of flour mixture to sugar mixture; beat just until combined. Add buttermilk mixture, then finish with remaining flour mixture.
Using an electric hand mixer with clean and dry beaters, beat egg whites and cream of tartar in a clean bowl at high speed until stiff peaks form. Using a spatula, carefully fold egg whites into the cake batter in 2 additions. Spoon batter evenly into cups and bake 20-22 minutes, until a toothpick inserted in the center comes out with a few moist crumbs attached. Cool the tea cakes for 2 minutes in the pans on a wire rack, then carefully remove from pans and place them on the wire rack to cool completely.
For the glaze:
Whisk together powdered sugar, tangerine zest, and juice in a small bowl. Set rack with tea cakes over a piece of wax paper and dip tops of each cake into glaze; let glaze set before serving. Store leftovers in an airtight container at room temperature up to 2 days.
(Recipe adapted from Cooking Light.)