FRESH SHRIMP: Add fresh shrimp and water to the Instant Pot. Place lid on Instant Pot and make sure valve is set to seal. Press the pressure cook button and set to high, then cook for 0 minutes (yes, you read that right! The Instant Pot will just come to pressure, then turn off).
FROZEN SHRIMP: Add frozen shrimp and water to the Instant Pot. Place lid on Instant Pot and make sure valve is set to seal. Press the pressure cook button and set to high, then cook for 1 minute.
Whether using fresh or frozen, do a quick release of the pressure on the Instant Pot by flicking the switch at the top with a spoon. Open the lid when pressure gauge has dropped and the lid opens easily.
Using oven mitts, drain shrimp and set aside on a platter. Place empty pot back inside the Instant Pot, then turn Instant Pot to saute mode.
Once hot, add butter, stirring until melted. Add lemon juice, garlic, dijon, chili flakes and salt and pepper to taste, stirring occasionally for 1-2 minutes until sauce thickens.
Drizzle sauce over shrimp, then garnish with fresh basil. Serve and enjoy!