Smash the garlic to peel off the skin easily and chop it finely. Set aside.

Remove the stem of the red chili and chop it finely. Set aside. (Make sure to wash your hand with soap and water after handling the chili.)

Prepare the prawns. Hold the prawn and gently pull the head off. Set it aside as we are going to use it later. Peel away the shell and legs in segments, keeping the tail on. Take the top of a knife and make a vertical incision at the back of the prawn. This will expose the vein that runs through the prawn's back. Remove the vein. Lay the prawn on the cutting board. Cut the tip of the tail and scrape the tail. Then make small cuts in the prawn's abdomen. Set aside.

Prepare the annatto infused oil. Heat the pan and add the cooking oil. Add the annatto seeds, stir to color the oil and bring to boil. When it boils, take the pan off the stove to avoid the seeds from burning and strain it. Set aside the oil and discard the seeds.

Heat the same pan in high heat and add the annatto-infused oil.
Add in the chopped garlic and red chili and sauté.
Turn down the heat and then add the head of the prawns. Mix and continue cooking until it turns orange in color.
Squeeze the head with a spatula to release the fat. The fat will give this recipe additional savory flavor.
Remove and discard the head; leaving the cooked garlic and red chili.

Add the butter in the pan and mix well to melt.
Add in the prepared prawns and season with salt and pepper. Make sure to coat the prawns with the sauce by turning it on all sides. Turn up the heat to high and cook the prawns evenly.