Preheat your oven to 350F. Grease a 9x13 inch baking pan. In a small bowl, whisk together the flour and baking powder and set aside.
In a large bowl, beat the egg yolks with the granulated sugar using an electric mixer until thick, pale, and ribbony, about 3-4 minutes. Mix in the whole milk and vanilla extract on low speed until combined.
In a separate clean bowl with clean beaters, beat the egg whites until stiff peaks form. Gently fold the flour mixture into the yolk mixture until just combined, then fold in the whipped egg whites in two additions, being very careful not to deflate the batter.
Pour the batter into the prepared pan and smooth the top. Bake for 25-30 minutes until golden and a toothpick inserted in the center comes out clean. Let the cake cool completely in the pan.
Whisk together the sweetened condensed milk, evaporated milk, heavy cream, and vanilla extract until combined. Poke holes all over the cooled cake using a fork, then slowly and evenly pour the three-milk mixture over the entire surface. Cover and refrigerate for at least 4 hours, or overnight for the best results.
When ready to serve, beat the heavy whipping cream, powdered sugar, and vanilla extract together with an electric mixer until stiff peaks form.
Spread the whipped cream generously and evenly over the soaked cake. Dust lightly with ground cinnamon, slice, and serve cold.