Make the cake: Preheat the oven to 350°F. Liberally grease a 9x13-inch baking pan with cooking spray, olive oil, or butter and set aside.
In a large bowl, combine the flour, baking powder, cinnamon, and salt.
In a medium bowl, beat together the egg yolks and ¾ cup of the granulated sugar on high using a handheld or stand mixer for about 1 minute until the yolks are pale yellow in color. Add the vanilla extract and whole milk and mix again until just combined.
Pour the wet ingredients into the dry ingredients and mix together until just combined to form a batter.
In another large bowl, beat the egg whites and remaining ¼ cup of granulated sugar on high speed using a handheld or stand mixer until shiny and stiff peaks form.
Gently fold the stiff egg whites into the batter with a silicone spatula, scraping the sides and bottom of the bowl as needed, until just combined and no white streaks remain.
Pour the batter into the prepared pan and bake for 30 to 35 minutes, or until a toothpick inserted into the center comes out clean. Set aside to cool to room temperature, then poke holes all over the cake with a fork or a skewer.
Make the milk mixture: Whisk together the whole milk, sweetened condensed milk, and evaporated milk in a medium bowl.
Slowly pour the three milk mixture all over the top of the cake. Cover and refrigerate for at least 2 hours, preferably overnight, to let the cake fully cool and absorb the liquid.
Make the whipped topping: Beat the heavy cream, sugar, and vanilla extract in a large bowl on high using a handheld or stand mixer until stiff peaks form. Cover and refrigerate until ready to serve.
Spread the whipped topping all over the cake. Garnish with dusting of cinnamon and sliced strawberries if desired.
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Notes
To make the sponge cake light and airy, the crucial step is beating the egg whites until shiny peaks form and then gently folding them into the cake batter. The air bubbles and volume of the egg whites help keep the sponge fluffy and light, even after soaking in the three-milk mixture.