Preheat oven to 320°F. Prepare a water bath: fill a pan that can accommodate the springform pan. Bring several cups of water to a boil.

In a bowl, over a pan of simmering water, combine vanilla, cream cheese, butter, and milk. Stir together until soft and creamy with no lumps remaining.

Sift flour and cornstarch together and vigorously whisk flour mixture with egg yolks and rosewater. Fold yolks into cream cheese mixture.

With a mixer, whisk egg whites, lemon juice, and salt until soft peaks form. Add sugar slowly until stiff peaks form. 

Fold whites into cheese mixture in 3 additions. Carefully pour batter into prepared pan and place into water bath. Place in oven and pour boiling water to a level of several inches, being careful not to get any water into the cake pan.

Bake for about 60 to 70 minutes or until a wooden skewer comes out clean and the top is lightly browned.

Remove cake from water bath and cool. Unmold cake and sprinkle with powdered sugar or drizzle with White Chocolate Ganache.

White Chocolate Ganache (optional):

Place finely chopped chocolate in small heatproof bowl. Set over warm water on low heat (water should not touch bottom of bowl). Stir very frequently until almost melted. Remove from heat and stir until smooth

In small saucepan over low heat, heat cream just to a simmer, stirring frequently. Remove from heat, add about two-thirds of hot cream to melted white chocolate. Gently stir to incorporate, until smooth, scraping bowl as necessary with silicone spatula. Gradually stir in remaining cream.

Pour ganache over cooled cake and allow to drip lazily down the sides of the cake.