Marinate the crabs and keep aside.
Take a deep bowl/utensil and add 3 cups water. Heat it.
After bubbles start appearing in water, add marinated crabs and boil them. (This typically takes around 8 -10 minutes).
Remove the boiled crabs from water and keep on a plate.
Heat a kadai and add butter.
Once butter melts, add finely chopped garlic.
After the raw smell of garlic goes away, add black pepper powder and garlic powder and mix well.
Add boiled crabs and mix well.
Serve hot.