Japanese Cheesecake (日式起司蛋糕)

A newly opened bakery in a nearby shopping mall is literally "selling it [the Japanese Cheesecakes] like hotcakes" :-).  Pa Pa's interest in making it at home was perked up, partly because grandma likes it a lot, partly because it tastes quite like the Italian Sponge Cake and Swiss Roll he made in a previous post.  His interest was finally set into action when we saw the price tag in the mall the other day :-).  BTW, most, if not all, Chinese bakeries sell Japanese Cheesecakes, a fact unknown to Pa Pa until recently, because buying cakes wasn't on Pa Pa's "Honey-Do List" in the past 3-4 decades :-).

Lots of recipes for Japanese Cheesecake are available online, most in English, almost all using similar methods (see link1, link2, link3 as examples).  One excellent page stands out as it comes with a great troubleshooting guide, a lifesaver for mere mortals like Pa Pa.  We also received great recipes from friends, one from Master Pastry Chef Shirley, the other from a good friend of our daughter's, Vickie. To our surprise, both recipes from our friends use cornstarch only, without adding any cake flour (unlike the online recipes cited above).  We followed this practice below, which yields silkier and smoother cake. The method used here is quite similar to that used in the previous post on Italian Sponge Cake and Swiss Roll, except for the water-bath baking at the end. 

1. [Prep Work] Take 6 eggs and 1 pack of 8-oz cream cheese out of the fridge, and leave them in room temperature for 30 minutes. Line the bottom of an 8" (8x3 round) cake pan, or two 6" (6x3 round) cake pans, with parchment paper (lightly oil the side of the pan with shortening or vegetable oil).  Take the cream cheese out of its 8-oz package, place it in a microwave-safe medium-sized glass bowl (e.g., Anchor Hocking 7-cup Glass Bowl), heat the cream cheese in microwave for 30 seconds, whisk, heat for another 15 seconds and whisk again.  Now, separate 6 egg whites from egg yolks (place egg yolks into the glass bowl with melted cream cheese, and egg whites into the bowl of a Stand Mixer).  Note- Do NOT use springform bake pan, because it’s very hard to make the pan waterproof for water-bath-baking later in Step 7. Consult this YouTube Video for more info on separating egg whites. 
2. Add 1/4 cup of milk, 1/4 cup of cream (or, 1/2 cup of Half and Half), 1/4 cup of veggie oil, and 1/3 cup of cornstarch, into the glass bowl with cream cheese and yolks. Whisk vigorously for 2-3 minutes (with a balloon-shaped whisk), until there is no clumps in the glass bowl. 
3. [Whip Egg Whites to Stiff Peaks] Turn on the Stand Mixer (using a Wire Whip), at low speed (Level 2-3 out of max-10), till the egg whites start to bubble, then to foam (1-2 minutes). [Optionally, but preferably,] add 1/2 tsp of white vinegar or Cream of Tartar.  Start to gradually add 1/2 cup of sugar (1/3 cup if you're sugar-conscious :-). Now, increase speed to 8 (max-10), if you want to speed things up a bit, till the egg whites show stiff peaks (~1.5 - 2 minutes.  Stop the mixer every 30 seconds or so, to check on the stiffness of egg whites with a spoon).  Note- Whipping to Soft or Soft-to-Medium Peaks works equally well, if not better (the stiffer the peaks, the more air whipped into the egg white, the thicker the cake after baking, and the more likely for the cake surface to crack during the cooling process). Cream of tartar helps in stabilizing the whipped egg whites in the baking process. Consult this YouTube Video for more info on separating and whipping egg whites. 
4. Scoop ~ 1/4 - 1/3 of the whipped egg white (with a spatula) into the glass bowl with cream cheese, egg yolks, and cornstarch (Step 3).  Stir and mix thoroughly (with a silicone spatula).  Note- This is to incorporate air bubbles into the egg yolk mixture, essential for the next step. 
5. Scoop all the mixture from Step 4 into the Stand Mixer bowl with the whipped egg white.  Use a silicone spatula to gently fold the egg whites up from the bottom of the bowl, to mix the whipped egg white with the egg-yolk-cornstarch mixture. Gently fold, in broad motions, until thoroughly mixed.
6. As part of the Prep Work in Step 1, we've lined the bottom of  an 8" cake pan, or two 6" cake pans, with parchment paper, and lightly oil the side.  Pour the batter (from Step 5) into the cake pan(s).  Gently spread the batter to the side of the pan and even the surface (with a spatula).  Shake the pan horizontally a fi iew times to further even the surface.  
7. [Water-Bath Baking] Preheat oven to 350-degF, and boil ~1 liter (i.e., ~4 cups) of water in a teapot.  Place the circular cake pan(s) in a 9"x13" (or larger) rectangular baking pan (with at lease 2.5" in depth).  Place the 9"x13" pan along with the cake pan(s) into the oven, at the bottom rack, and carefully pour the boiling water into the rectangular pan (now, the circular cake pan(s) is sitting in a water bath).  Bake until the surface of the cake turns slightly golden (~20-25 minutes). Decrease the ovenFor  temperature to 300-degF, and bake for another 45-55 minutes (after lowering the temperature down to 300-degF).  Cover the baking pan(s) with aluminum foil once the cake surface turns golden brown (to prevent the surface from turning out too dark).  Note- For two 6" cake pans, we baked at 350-degF for 25 minutes, and 300-degF for 55 minutes.  For one 8" cake pan, 20 minutes at 350-degF and 50 minutes at 300-degF.  As the online troubleshooting guide (cited above) and other experts suggested, under-baking might be a main reason for this cake (or any cake) to deflate, and for a cake's surface to wrinkle, after cooling off.  Try not to under-bake (err on the over-baking side!).  To check if the cake is done, gently press (or tap) on the cake surface with the fleshy side of a finger (i.e., the finger pulp).  The cake is done if the cake surface bounces right back to its original position. Otherwise bake 3 more minutes and check again. This is as reliable as, if not more so than, the "inserted toothpick coming out clean" test.
8. [Cooling down the Cake Gradually inside the Oven] Cooling down the cake inside the oven with the oven door closed for 20 minutes, and then, with the oven door ajar slightly (by inserting an oven glove between the oven door and the oven) for another 20 minutes. The cake surface might show wrinkles if it is cooled down rapidly. Take the rectangular baking pan out of the oven carefully, along with the circular cake pan(s) still sitting in the very hot water bath.  After further cooling of 15-20 minutes, take the cake pan(s) out of the water bath.  Leave the cake(s) in the fridge overnight, or 6-8 hours.  Before serving, separate the cake(s) from the side of the pan(s) with a thin knife, then flip the cake out of the cake pan(s) onto a flat plate, slowly remove the parchment paper from the bottom.  Flip the cake(s) again onto a serving plate. Cut and serve. Here is a picture of the outcome from our kitchen (with two 6" cake pans sitting in a water bath).