Preheat the oven to 350°F and butter a 13×9 inch metal baking pan.
In a medium-size bowl whisk together all purpose flour, baking powder, salt and 1/8 tsp ground nutmeg. Set aside.
In the bowl of a stand mixer cream together butter, cup sugar, egg yolks, and 2 tsp vanilla. Cream for 2-3 minutes.
To the bowl add the sifted dry ingredients alternately with the buttermilk. Stop to scrape the sides of the bowl as needed.
In a separate bowl whip the egg whites until stiff peaks form. Fold into the cake batter by hand. Pour batter evenly into the baking pan.
Bake for 28-30 minutes or until a toothpick inserted into the center comes back clean.
Rest for 20 minutes. Poke holes over the top of the cake with a fork or wooden skewer.
Tres Leches Filling
Whisk together the evaporated milk, sweetened condensed milk, 1/2 cup heavy cream, 1 tsp vanilla, and 1/8 tsp ground nutmeg.
Slowly pour 1/2 over the cake allowing it to seep into the holes then pour the remaining on top.
Cool to room temperature then cover and chill overnight.
Whip together the remaining 2 cup heavy cream with 1/4 cup granulated sugar. Frost the top with the whipped cream and dust with nutmeg. Serve with seasonal berries.