Preheat oven to 320°F. Line bottom of 9x3-inch round cake pan with parchment paper. Line sides of pan with a 4-inch wide strip of parchment. (You should have about 1 inch of paper extending above the top of the pan.) Set aside.
Test Kitchen Tip: To prepare using a 9-inch springform pan, line with parchment as directed in Step 1. Place pan in center of large sheet of heavy duty foil. Wrap, making sure bottom and sides are completely covered, to keep water from soaking into cake batter.
Beat egg yolks in large bowl with wire whisk; set aside. Mix cream cheese, butter and milk in small saucepan on medium heat until melted and smooth; remove from heat. Gradually add cream cheese mixture to egg yolks, stirring constantly with wire whisk. Stir in extract until completely smooth.
Sift flour and cornstarch into batter mixture, stirring constantly with wire whisk until well blended.
Beat egg whites and cream of tartar in separate large bowl with electric mixer on medium speed until soft peaks form. (If using a freestanding mixer, use wire whisk attachment.) Increase speed to medium-high. Gradually add sugar, beating until sugar is dissolved and stiff peaks form.
Gently stir in 1/4 of the egg white mixture into the batter mixture; repeat until fully incorporated. Pour batter into prepared pan and gently tap pan on the counter to remove any large air bubbles.
Place pan in large roasting pan or dish. Pour enough hot water into roasting pan to cover about 1 inch from bottom of cake pan. Bake 25 minutes. Reduce heat to 280°F. Bake 55 minutes longer or until cake has risen and the top is golden brown.
Remove from oven. Let stand in water bath until cool enough to handle. Remove from water bath. Invert cake onto large plate or cutting board to remove parchment paper. Carefully flip cake onto serving platter. Sprinkle top with powdered sugar and serve warm with fresh berries and whipped cream, if desired.