Combine flour, sugar, and baking powder in a mixing bowl until they're well incorporated
Add the milk and egg to the bowl then mix using a whisk or electric mixer at a medium speed until the batter becomes smooth.
Pour the water, butter, and vanilla extract then stir until the ingredients are well mixed.
Add the grated cheese and slowly fold it into the mixture using a spatula or spoon.
Grease each mold with butter and fill the molds with batter up to ¾ full.
On a very low heat, fill the bottom of the steamer with water and bring it to a gentle simmer.
Place the molds in the steamer basket and steam for about 10 to 12 minutes. You can check if they are ready by sticking a toothpick in the middle and seeing if it comes off clean.
Remove the lid and add a strip of cheese on top of each puto. Cover the steamer and let the puto steam for another minute or two until cheese melts.
Turn off heat and let the puto rest until they are slightly cooled down.
Remove the cooked Puto Cheese from the molds and transfer to a serving plate.