In a large bowl, stir the masa harina with the water until evenly moistened; let cool. In the bowl of a standing electric mixer fitted with the paddle, beat the lard with the baking powder and salt at medium speed until fluffy, about 3 minutes. With the machine on, add the masa in golf-ball-size lumps, then drizzle in the chicken stock and beat the masa until completely smooth. Increase the speed to high and beat until fluffy, about 3 minutes; the texture should resemble soft hummus.
Masa harina (nixtamalized corn flour) is available at supermarkets, specialty food shops and online at mexgrocer.com.