Whisk together the cake flour, baking powder, and salt.
In another bowl, whisk the sugar, eggs, melted butter, milk, water, and vanilla until combined.
Add the dry ingredients. Mix gently until no dry flour remains. Stir in the grated cheese. Add ube or pandan extract, if using.
Bring steamer water to a boil, keeping it below the rack. Wrap the lid with a clean towel secured away from the heat. Grease the molds and fill ¾ full.
Arrange the molds in the steamer with space between them. Cover and steam over medium-low heat for 12–15 minutes for small molds or 18–20 minutes for standard molds, until a toothpick comes out clean.
Top each puto with a cheese slice. Cover and steam for 1–2 minutes, until softened. Turn off the heat.
Cool for a few minutes, then remove from the molds. Serve warm.
Notes
Cake flour: Makes soft, light puto. All-purpose flour works but may make it denser.
Baking powder: Use fresh baking powder to help the puto rise.
Butter: Salted or unsalted works. Cool slightly after melting.
Milk: Use whole or evaporated milk.
Cheese: Eden, Quickmelt, American, or cheddar works. Grate for the batter and slice for topping.
Ube or pandan extract: Optional. Add a few drops for color and flavor.