In a large pot or saucepan, melt one stick of butter over medium-low heat. Add the Coriander Seeds, Thai Chilies, and Bay Leaves. Sauté for 1–2 minutes until the spices become fragrant.
Add the sliced Galangal, sliced Lemongrass, and chopped Garlic. Cook for another 2–3 minutes, stirring occasionally, until the garlic is softened.
Stir in the Old Bay Seasoning, Tom Yum Powder, and Chili Paste with Soya Bean Oil. Cook for just one minute to toast the spices.
Add the remaining stick of butter, Fish Sauce, MSG, and the chopped Scallions. Stir until the butter is completely melted.
Squeeze the juice from the lemon and lime halves into the pot. Add the squeezed fruit halves and simmer gently for one minute.
Strain out the bay leaves, lemon, and lime halves. Keep the liquid butter warm for serving.