Prepare the crabs: Clean the crabs thoroughly. If whole, cut them into serving pieces (quarters for smaller crabs, halves for larger ones). Ensure all parts are rinsed and patted dry.

Toast and grind the peppercorns: In a dry skillet over medium heat, toast the black and white peppercorns until fragrant, about 2-3 minutes. Let cool slightly, then coarsely grind using a mortar and pestle or spice grinder.

Make the sauce base: In a small bowl, whisk together the dark soy sauce, oyster sauce, honey, and water.

Sauté aromatics: Heat the sesame oil and butter in a large wok or skillet over medium-high heat. Add the grated ginger, minced garlic, and chopped chilies. Stir-fry until fragrant, about 1 minute.

Sear the crab: Add the crab pieces to the wok. Stir-fry for 3-4 minutes until they start to turn red and are lightly seared.

Add spice and sauce: Sprinkle the ground peppercorns over the crab. Pour in the prepared sauce mixture. Toss well to coat the crab evenly.

Simmer and thicken: Bring the sauce to a simmer. Cook for 5-7 minutes, or until the crab is cooked through. Stir in the cornstarch slurry to thicken the sauce to your desired consistency.

Garnish and serve: Stir in most of the chopped scallions and cilantro. Transfer the crab to a serving platter and garnish with the remaining scallions and cilantro. Serve immediately.