Preheat the oven to 350°F. Butter and flour a 13 x 9 inch metal baking pan or spritz with baking spray.
Cake: In a medium-size bowl, use a whisk to sift together all purpose four, baking powder, salt and 1/8 tsp ground nutmeg. Set aside.
In the bowl of a stand mixer, cream together butter, 1 cup sugar,egg yolks, 2 tsp vanilla and 1 tsp rum extracts. 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 then 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.
For the filling: Whisk together the evaporated milk, sweetened condensed milk, 1/2 cup heavy cream, 1 tsp vanilla and 1 tsp rum extract and 1/8 tsp ground nutmeg.
Pour 1/2 over the cake allowing it to seep into the cake, then pour the remaining on top.
Cool to room temperature then cover and chill overnight.
To serve, whip together the remaining 2 cup heavy cream with 1/4 cup granulated sugar and 1/2 tsp rum extract. Adjust sweetness taste.
Frost the top with the whipped cream, dust with nutmeg and serve with seasonal berries.
Store leftovers chilled.