Grease two 8x1-1/2-inch round baking pans. Line the bottoms with waxed paper or parchment paper. Grease the paper. Lightly flour pans; set aside. Place half the pecans in a blender container or food processor bowl. Cover; blend or process until coarsely ground. Repeat with remaining nuts. Combine pecans, flour, and baking powder in a mixing bowl.
Place eggs and granulated sugar in a blender container or food processor bowl. Cover; blend or process until smooth. Add nut mixture. Cover; blend or process until smooth, stopping to scrape sides as needed to mix evenly (mixture may be foamy). Spread evenly in prepared pans.
Bake in a 350 degree F oven for 25 to 30 minutes or until lightly brown and tops spring back when lightly touched (centers may dip slightly). Cool in pans on wire racks for 10 minutes. Remove from pans; cool thoroughly on racks.
For tangerine filling, beat cream cheese and butter in a medium mixing bowl with an electric mixer on medium to high speed until fluffy. Gradually add brown sugar, beating for 3 to 4 minutes or until smooth. Stir in citrus peel and vanilla.
To assemble, with a serrated knife, cut cakes in half horizontally. Place one cake layer, cut side up, on a platter. Spread one-third of the filling on the cake. Place another cake layer, cut side down, atop filling. Spread top with another one-third of the filling. Add a third cake layer, cut side up, followed by the remaining filling and the final cake layer, cut side down.
In a medium chilled mixing bowl, combine whipping cream, sugar, and finely shredded tangerine or orange peel. Beat with chilled beaters of an electric mixer on medium speed until soft peaks form. Do not overbeat.
Frost top and sides of the cake with whipped cream mixture, reserving some of the frosting for piping, if desired. Place the reserved frosting in a decorating bag fitted with a large star tip. Pipe frosting atop cake in a ring. If desired, decorate with orange peel curls and edible roses. Refrigerate frosted cake for up to 4 hours. Makes 12 servings.