In a bowl, combine egg yolks, condensed milk and vanilla. Stir until well blended. Set aside.
Prepare steamer by putting in water until base is half-filled. Turn on heat to high until water boils.
Fill each puto mold with 1-1/2 tsp of leche flan mixture. Steam for 5 minutes.
Meanwhile, combine flour, baking powder and sugar in a bowl. Add water and mix until smooth. Fill each puto mold half full with cooked leche and steam again for 15 minutes. Cool and invert cooked puto leche on a serving plate.