1. Preheat oven to 325°F. Mix flour, baking powder, rosemary and salt in small bowl. Butter and flour 9-inch springform pan. Slice Brie evenly into 3 horizontal layers. Place 1 layer, skin-side down, in center of bottom of prepared pan. Cut remaining 2 layers in half. Place, skin-side down, around Brie in pan so that most of the bottom of the pan is covered with Brie, leaving about 1/2-inch uncovered around edge of inside of pan. Set aside.
2. Beat butter and 1/4 cup of the sugar in large bowl with electric mixer on medium-high speed 3 to 4 minutes or until light and fluffy, scraping sides of bowl occasionally. Add egg yolks, beat on high speed until well blended, scraping sides of bowl occasionally. Beat in 1/2 of the flour mixture, milk then remaining flour mixture on low speed until well blended, scraping sides of bowl occasionally.
3. Beat egg whites in clean large bowl with electric mixer on high speed 2 minutes or until soft peaks form. Mix remaining 1/2 cup sugar and cream of tartar in small bowl. Gradually beat into egg whites until stiff peaks form. Stir 1/3 of the egg white mixture into egg yolk mixture until well blended. Gently stir or fold in remaining egg white mixture. Pour and spread batter over Brie to create an even cake layer.
4. Bake 30 to 35 minutes or until toothpick inserted in center comes out clean. Run small knife or metal spatula around rim of pan to loosen cake. Cool about 30 minutes in pan on wire rack. Remove rim of pan. Spread top of cake evenly with preserves. Serve warm. Refrigerate any leftover cake.
To Make Ahead: Prepare and bake cake as directed above. Cool completely. Cover tightly. Refrigerate. Several hours before serving, remove cake from refrigerator and bring to room temperature. Remove rim of pan. Place cake on baking sheet. Spread top of cake evenly with preserves. Heat in preheated 350°F oven 15 to 20 minutes or until warmed through.