Line puto molds with cupcake liners. Set aside.
Sift the cake flour and baking powder in a big bowl. Set aside.
In a separate big bowl, beat the egg whites at low speed until it becomes bubbly. Add cream of tartar, if using. Continue to beat at low speed until it turns foamy. While beating, still at low speed, gradually add the sugar. Once all sugar is added, increase speed to medium and beat until medium/firm peaks are formed. Set aside.
Back to the other bowl, gradually add the milk to the dry ingredients while mixing until it reaches a pancake-batter-like consistency. You may need to adjust the amount of milk to achieve this.
Take ⅓ of the meringue and add it to the batter. Whisk to lighten the batter so it will not deflate the meringue. Add the rest of the meringue in two batches, carefully folding each batch into the batter until well blended. Do not over-fold of the meringue will deflate.
Fill the lined molds with puto mixture half-way full. Spoon some of the pork Asado in the middle of each mold. Then fill it again with puto mixture to cover until ¾ of the liner is filled. Add a slice of salted egg.
Fill the bottom of the steamer with tap water. Place the steamer basket on top and arrange the puto molds inside it. Turn the heat on and bring the water to a very gentle simmer over very low heat. Steam until an inserted toothpick comes out clean, about 25-30 minutes. Turn off the heat and let it rest and cool down a bit.
Transfer the puto pau to a cooling rack. Enjoy while still slightly warm or wait until completely cool. If you have leftovers, you may store them in a container and refrigerate for a couple of days, Re-steam in a steamer, or just reheat in a microwave.