Before starting, cut your chicken thighs into 1-inch cubes. Make sure they're all about the same size so they cook evenly. Mince your garlic, ginger, and onions. Remove stems from Thai chili peppers and slice your finger chilies.
Heat oil in a deep pan over medium heat. Add your minced garlic, ginger, and onions. Cook until the onions become clear and you can smell the garlic, about 3-4 minutes.
Put in your chicken pieces. Let them cook until they turn light brown, stirring every now and then. This takes about 8-10 minutes.
Add the shrimp paste. Keep stirring for 1-2 minutes to coat all the chicken pieces evenly.
Pour in your coconut cream and add the Thai chili peppers. Very important: Keep the heat medium-low so the sauce only gently bubbles, never let it boil hard or the coconut cream will separate.
Cover your pan and let everything cook gently for 20-25 minutes. You'll know the chicken is done when cutting into a piece shows no pink inside.
Add your sliced finger chilies and cook for 2-3 more minutes, just until they soften a bit. Taste the sauce and add salt and pepper until it tastes right to you.
Let everything rest for a few minutes before serving. The sauce will get slightly thicker as it cools. Serve hot with plenty of rice.
Remember: If you want the dish less spicy, remove the seeds from the chilies before cooking. If you want it spicier, leave them in. You can always serve extra chilies on the side for people who want more heat.
Tip: Watch your coconut cream carefully - keep the heat gentle and you'll get a smooth, creamy sauce. Too much heat will make the sauce separate and become grainy.