Soak corn husks in warm water until soft, about 1 hour. Drain and throughly dry corn husks.
Cover chicken with water in 4-quart saucepot. Bring to boil over medium-high heat. Reduce heat to low and simmer until chicken is thoroughly cooked, about 30 minutes. Remove from chicken from saucepot. Cool, then shred; set aside.
Toss tomatillos, onion and serrano pepper in oil and broil until evenly charred, turning occasionally; allow to cool slightly. Process vegetables, 1 tablespoon Knorr® Chicken flavor Bouillon and garlic in blender or food processor until smooth. Cook processed vegetables with shredded chicken in 12-inch skillet low heat, stirring occasionally, until thickened and excess water has cooked out, about 5 minutes.
For masa dough, dissolve remaining Bouillon in boiling water. Pour water into mixing bowl, then stir in masa harina and baking powder. Beat on medium speed using paddle attachment, until combined. Remove from bowl and set aside. Beat lard on high speed in same bowl until very fluffy. Reduce speed to medium, then add masa mixture, a handful at a time, until mixture is smooth and well combined. Increase speed to high and beat until masa is a soft, thick paste, about about 4 minutes. Cover and set aside.
Spread 1/4 cup masa dough onto each husk. Place 2 tablespoons chicken filling on the middle of the masa dough. Fold sides of corn husk to center, wrapping the filling. Fold one end of corn husk up against the seam to seal.
Arrange tamales vertically in steamer basket over a pot over boiling water, top with extra husks. Cover with lid and steam until husks pull away from filling, about 45 minutes. Check water level often and add additional water as necessary to avoid burning tamales. Cool tamales 3 minutes before serving.