Preheat oven to 320
Place cookie sheet in oven with water. Place rack inside cookie sheet.
Grease springform pan and put parchment on bottom
Wrap springform pan with foil
Melt the following in pot:
4 tablespoon butter
3 oz cream cheese
1/4 cup milk
Set aside to cool
Separate 4 eggs
Beat egg whites with 1/3 cup sugar until stiff peaks
Add to butter mixture
2 tablespoon rice flour
2 tablespoon potato flour
3 tablespoon cornstarch
1 tablespoon orange or lemon zest (optional)
Add yolks to flour/butter mixture
Add 1 teaspoon vanilla extract
Fold mixture into egg whites
Pour into greased springform pan and bake at 320 for 25 minutes
Reduce heat to 285 and bake additional 50 minutes until center is set
Let sit on counter for 5 minutes and gently slide spatula to separate cake from pan before releasing spring.
Place on plate to cool
Sprinkle with powdered sugar