• Preheat the oven to 350°F. Butter just the bottom of a 13-by-9-inch pan, leaving a ¼-inch border ungreased. Do not butter the sides of the pan. This helps the cake “climb” up the sides while it bakes.
• Add the room temp egg whites to a large mixing bowl. Use the whisk attachment on a stand mixer or hand mixer beaters to beat on high speed until foamy and doubled in size, about 1 minute. Continue to beat while slowly pouring in ¼ cup sugar. Beat until stiff peaks form, about 3 minutes. Set aside.
  6 large eggs , ¼ cups granulated sugar
• In a separate large mixing bowl add the egg yolks and 1 cup sugar. Beat on medium speed, with paddle attachment or hand mixer, until pale and fluffy, about 2-3 minutes. Beat in the milk and vanilla. Add the flour, baking powder, and salt. Beat well, about 1 minute. The batter will be very thick.
  ½ cup whole milk, 1 teaspoon vanilla extract, 2 cups gluten-free all-purpose flour, 2 teaspoons baking powder, ½ teaspoon salt, 1 cups granulated sugar
• Using a spatula, fold half the egg whites into the flour mixture. Finish with the second half, until no white streaks remain. It will be hard to work in at first, but as the whites work in the batter will loosen up. Spread the batter into the cake pan and let rest for 15 minutes. This helps the moisture soften the GF starches and build the structure of the cake so it doesn't sink.
• Bake for 30 minutes or until a toothpick or cake tester inserted into the center comes out clean. Let the cake cool until slightly warm, about 30-45 minutes.

Milk Soak and Frosting

• In a medium bowl whisk together the condensed milk, evaporated milk, whole milk and vanilla. Poke the cake all over with a fork or wooden skewer, all the way to the bottom. Slowly pour the milk over the cake. It won't soak all the way through at first, but will eventually absorb. Cover and chill for at least 4 hours, but overnight is best.
  14 ounces can sweetened condensed milk, 12 ounces can evaporated milk, ⅔ cup whole milk , 1 teaspoon vanilla extract
• Wait to make the whipped cream frosting the day you will be serving. Add the chilled heavy cream and powdered sugar to a large mixing bowl. Use the whisk attachment on stand mixer or hand mixer beaters to mix on medium-high speed until medium peaks form.
  2 cups heavy whipping cream , 3 tablespoons powdered sugar, cinnamon
• Spread the frosting over the cake and then dust with cinnamon. Keep refrigerated up to 2 days.