For Cake:

• Preheat oven to 350ºF with oven rack positioned in the middle if you have a large oven, or with racks at top and bottom third positions if oven is too small to comfortably fit two 9" pans without touching sides of oven or each other.  Grease and flour two 9x2" round cake pans and line bottoms with circles of parchment paper.  Set aside.
• Place egg whites in stand mixer with whisk attachment and beat on medium-high speed until soft peaks form. Gradually pour in 1/4 cup (50 g) of the sugar then increase speed to high and continue beating until glossy stiff peaks form. Scrape the beaten whites into a bowl and set aside. Give mixer a rinse and dry (no need to properly wash it, but toss the towel in the laundry because raw eggs).
  
• Measure sugar, flour, baking powder, baking soda and salt into the mixer bowl (quick and easy if you put the bowl right on the scale). Switch to paddle attachment and beat the dry ingredients on medium-low speed for 1 minute (this replaces sifting to aerate and thoroughly combine).
• Toss in the chunks of soft butter and beat, starting on low until the mixture goes from lumps of butter to even small crumbs. The flour will fly if the mixer speed is too high while butter chunks are large, but you can increase it as they get smaller.
  
• Meanwhile, whisk together the yolks with the milk, oil, sour cream, vanilla and almond (if using) extract.
• Reduce mixer speed to low and drizzle in 1/2 the milk mixture. Scrape down the sides of bowl and paddle after just a few seconds, then beat on medium (no higher) until smooth, about 15 seconds. Reduce speed to low and drizzle in remaining milk mixture then gradually increase speed to medium until evenly combined. The batter may look a bit curdled, not smooth, and that's normal.
• Remove bowl from stand mixer and use a large rubber spatula to fold 1/2 of the beaten egg whites into the batter until mostly incorporated but still streaky. (This lightens the batter making it easier to gently incorporate the rest.) Gently fold in remaining egg whites until no white streaks remain.
  
• Divide batter evenly between the two prepared baking pans and smooth the tops. (I put the pans back on the scale to ensure they both have the same amount of batter for consistency in baking time).
• Bake cakes for approximately 35-45 minutes, swapping position of cake pans halfway through. The cake is done when internal temperature in the centre of the cake registers 190ºF with a cooking thermometer.

  **NOTE: See further doneness-testing details in blog post. Baking time is given as a wide-range estimate as ovens vary in temperature accuracy, baking pans vary in heat conduction, opening the oven can add minutes, and if your ingredients are not room temperature, this also adds to baking time. Also if one pan has more batter than the other, it will take longer. Mine took 34-36 minutes, but some readers have reported back that the full 45 minutes were needed. Use a thermometer for accuracy.
• Let cool 10 minutes in pans placed on cooling racks before running a knife around the cake edges and flipping them onto parchment-lined cooling racks (use parchment so the moist cake doesn't get stuck to the rack). Cool completely before filling and frosting.