Follow the sautéing instructions in a 2-liter pressure cooker. For spicy mushroom biryani, add 1.5 to 1.75 cups water. For the Chettinad style biryani, add 1 cup coconut milk and ½ to ¾ cup water. Season with salt. Pressure cook on medium to medium-high heat for 2 to 3 whistles or 8 to 9 minutes. When the pressure falls naturally in the cooker, open the lid. Fluff and serve.