Wash shrimp and remove heads. Return shrimp, except the heads, to the fridge.
Select SAUTÉ-High and set the time for 30 minutes. Press START. Add canola oil to the Inner Pot.
When the oil is hot, sauté shrimp heads until light golden, around 5 minutes.
Add water to pot to prepare shrimp stock. Press CANCEL when the water starts to simmer.
Select SLOW COOK-High and set the time to 1 1/2 hours. Press START. Close the lid and set to VENT.
Cut the top and bottom end of the lemon grass. Crush all the surface with the back of the knife to infuse stock with flavor. Cut in 1-inch length pieces and add to pot.
Add galangal pieces, teared kefir lime leaves, and chili pepper pieces to pot.
Let the stock cook for 45 minutes.
In the meantime, cut the back of the shrimps with a small kitchen scissor or knife. Clean the black vein if there is any. Take them back to the fridge.
Tear mushrooms lengthwise to 2-3 pieces.
Juice the limes.
After 45 minutes, strain the stock and return the liquid to the pot. Discard the vegetables. Lime leaves, chili pepper and shrimp heads can be used for plate decoration.
Add shrimp paste, red curry paste, fish sauce, sugar, lime juice. Stir. Taste and adjust these ingredients according to your preference.
Add mushroom and sprinkle shrimps on top. Close the lid and let them cook for 30 minutes.