How to Make It
Preheat oven to 350°F. Melt butter in a 10-inch cast-iron skillet over medium-low heat; sprinkle brown sugar over butter. Remove from heat. Arrange figs, cut sides down, over sugar mixture; sprinkle with walnuts.
Beat 3 egg yolks at high speed with an electric mixer until thick and pale; gradually add 1 cup granulated sugar, beating well. Stir together flour and next 4 ingredients; add to egg mixture alternately with milk, beginning and ending with flour mixture. Stir in vanilla.
Beat egg whites at high speed with an electric mixer until stiff peaks form; fold egg whites into batter. Pour batter over figs in skillet.
Bake at 350°F for 38 to 40 minutes or until a wooden pick inserted in center comes out clean. Cool in skillet on a wire rack 10 minutes; invert cake onto a serving platter, scraping any syrup from bottom of skillet onto cake.
Beat whipping cream and port, if desired, until soft peaks form. Serve cake warm or at room temperature with whipped cream.