1. Bake the Cake:

1. Separate eggs while cold, placing yolks in one bowl and whites in another. Let sit at room temperature for 30 minutes.
2. Preheat oven to 350°F. Grease a 9×13-inch baking pan and set aside.
3. In a bowl, whisk together flour, baking powder, and salt.
4. Using an electric mixer, beat egg whites and cream of tartar for about 2 minutes until stiff peaks form. Set aside.
5. In a separate bowl, beat egg yolks for 2 minutes until thick. Gradually add sugar in three batches, beating for another 4 minutes until thick and ribbon-like.
6. Add ½ cup milk and beat briefly until combined.
7. Using a spatula, fold in the flour mixture in two additions. Then, gently fold in beaten egg whites until just combined.
8. Pour batter into the prepared pan and bake for 20 to 23 minutes, or until a toothpick inserted in the center comes out clean. Let cool completely on a wire rack.

2. Prepare the Coffee Milk:

1. Warm 1 ½ cups milk on the stovetop or microwave (do not boil).
2. Stir in instant coffee and let it cool to room temperature.
3. Once cooled, mix in ¾ cup heavy cream, sweetened condensed milk, rum (if using), and vanilla extract.

3. Soak the Cake:

1. Once the cake is fully cooled, poke holes all over the surface using a fork or toothpick.
2. Slowly pour the coffee milk mixture evenly over the cake.
3. Cover with foil and refrigerate overnight.

4. Make Mascarpone Whipped Cream & Assemble:

1. In a large bowl, beat heavy cream, confectioners’ sugar, mascarpone, vanilla extract, and salt until thick and creamy.
2. Spread evenly over the chilled cake.
3. Dust cocoa powder over the top using a fine strainer.
4. Cover and refrigerate for a few hours before serving.