To caramelize carrots in a pressure cooker, Nathan Myhrvold adds a bit of baking soda: It increases the pH, which speeds up the Maillard (browning) reaction. More Carrot Recipes
In a pressure cooker, combine 6 tablespoons of the butter with the carrots and cook uncovered until the butter is melted. Stir in the salt and baking soda, cover and cook at 15 PSI (see Note) for 10 minutes. Place the pressure cooker in the sink and run cold water over the lid to depressurize it rapidly; remove the lid once it can be released without force.
Add the carrot juice to the cooker and stir to release any caramelized bits stuck to the pot. Return the cooker to medium heat, uncovered, and rewarm the contents. Transfer the contents of the cooker and the remaining 2 tablespoons of butter to a blender and puree until smooth. Season the soup with pepper and pour into bowls. Garnish with the ginger, tarragon and caraway seeds and serve.
Fifteen pounds per square inch (PSI) is the most common setting for pressure cookers. Products vary, however, so be sure to consult the owner's manual.