We will start by preparing the ingredients for the curry paste. Start by preparing the lemongrass by peeling off the outer few layers and cutting off the leafy top half of the stalk. Thinly slice the white stalky portion of the remaining stalk -- you should see smaller purple-color circles on the inside of the slices. Slice until the purple color stops.
Mince the shallot, galangal, and ginger. Remove the cilantro roots. Fold the kaffir lime leaves in half along the stem and de-stem before slicing.
Combine all the curry paste ingredients (except for the turmeric, as we don't want to stain our mortar and pestle) into a mortar and pestle and begin grinding until you get a rough paste. If you don't have a mortar and pestle, a blender will also work.
Next, we will prepare the stir fry ingredients. mince the garlic and shallots and slice the mushrooms, scallions and chili pepper. Heat a skillet and spray cooking oil. Begin by adding the curry paste and add in the turmeric at this time to add the yellow color. Adding in the turmeric at this step prevents you from staining the mortar and pestle. Keep stirring the ingredients in the pan to prevent burning.
Begin to add in the vegetables and crab meat, cooking for about 3-4 minutes or until the vegetables have softened. Add in water as needed to deglaze the pan and help mix the curry paste throughout the dish. Season with fish sauce and sugar as needed, tasting and adjusting until you achieve your desired taste.
Turn heat to low and crack in an egg. Mix thoroughly with the rest of the dish. This will give the dish a delicious creamy egg like texture.
Remove the dish from heat, garnish with cilantro and/or Thai basil, and enjoy your delicious protein and flavor packed crab curry!