Separate egg yolks from whites. Allow eggs, butter, and sour cream to stand at room temperature for 30 minutes. Meanwhile, grease and lightly flour a 10-inch fluted tube pan. Set aside. In a medium bowl, combine flour, baking powder, baking soda, salt, and nutmeg. Set aside.
In a large mixing bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Gradually add the 1-3/4 cups granulated sugar, beating about 10 minutes or until very light and fluffy. Add egg yolks, one at a time, beating 1 minute after each addition and scraping bowl frequently. Beat in tangerine juice and vanilla. Add flour mixture and sour cream alternately to beaten mixture, beating on low to medium speed after each addition just until combined. Stir in tangerine peel.
Thoroughly wash beaters. In another large mixing bowl, beat egg whites with an electric mixer on medium speed about 1 minute or until soft peaks form (tips curl). Gradually add the 1/4 cup granulated sugar, 1 tablespoon at a time, beating on high speed about 4 minutes more or until mixture forms stiff, glossy peaks and sugar dissolves. Immediately fold half of the whites into batter, then fold in remaining whites (batter will be very thick). Spoon batter into prepared pan.
Bake in a 325 degree F oven for 65 to 75 minutes or until a wooden toothpick comes out clean. Cool in pan on a wire rack for 15 minutes. Remove from pan and place on wire rack set over waxed paper. Brush warm Tangerine Glaze all over warm cake. Cool completely. Sprinkle with powdered sugar before serving, if you like. Serve with Sweetened Tangerine Whipped Cream or creme fraiche and berries, if you like. Makes 16 servings.
Prepare cake. Wrap well and store in refrigerator up to 2 days. Bring to room temperature before serving.
In a chilled medium bowl beat whipping cream and powdered sugar with an electric mixer on medium speed until soft peaks form. Fold in tangerine peel. Makes 2 cups.
In a small saucepan, combine sugar and tangerine juice. Bring to a simmer, stirring till sugar dissolves. Makes about 1/2 cup.