Combine all the ingredients for the spice paste in a blender jar or a food processor. Blend/ process to a smooth paste. This paste can be stored in the refrigerator for 2 weeks or in the freezer for couple of months.
Make Soup - Instant Pot Method:
Turn the Instant pot on 'Saute' mode (default 'Normal' - not high or low). Add oil and once it heats up add onion and carrot and cook for 3~4 minutes or until the onions turn translucent.
Stir in the ground spice paste and cook for 2 minutes. Next add the rinsed and drained split peas, coconut milk, water and salt.
Turn off the Sauté function by pressing 'Cancel'.
Close the lid of the Instant pot and cook on Manual/ High Pressure for 15 minutes. Make sure that the vent is in sealing position.
Once the time is up, let the pressure release naturally for 15 minutes and then do a Quick pressure release.
Stir in chopped spinach and cilantro. Mix well. The residual heat is enough for the greens to wilt. Taste and adjust the seasoning. Serve hot.
Use about 2-3 ribs of lemon grass to get ¼ cup of coarsely chopped flesh.
You can use store bought tom yum paste or red curry paste instead of making the spice paste to save time.
Spice paste can be made up to 2 weeks in advance. Store in an airtight container in the fridge. Or you can freeze it for up to 2 months.
If making the recipe in a pressure cooker, then cook for about 3~4 whistles.
If cooking in open pot, then bring the mixture to a boil and reduce the heat. Cover and cook for 45 mins ~ 1 hour or until split peas are completely soft.
This Thai split pea soup can be stored in the fridge for up to 3 days and in the freezer for up to 2 months.