In a large heatproof bowl, stir together the light soy sauce, dark soy sauce, oyster sauce and Shaoxing wine. Add the chopped garlic and grate the ginger directly in and stir to combine.
Place the chicken leg and drained shiitake mushrooms in the marinade, tossing to cover evenly.
Leave to marinate for at least 30 minutes, and up to overnight.
Push the chicken leg and mushrooms to the side of the bowl, and add the drained soaked glutinous rice, as well as 60ml of the mushroom soaking water.
Stir to mix the marinade, glutinous rice and mushroom soaking water.
Place the chicken leg, skin side up,back on top of the rice, and arrange the mushrooms around it.
Steam for 45 minutes, until the chicken and rice are both cooked through.
Top with white pepper and serve.