Prepare Instant Pot: Heat up Instant Pot by pressing Sauté button to go to Sauté Normal Function. Make sure your pot is as hot as it can be (Instant Pot: wait until the indicator says HOT).
Saute Veggies: Pour 1 tbsp (15ml) olive oil & 2 tbsp (28g) unsalted butter in Instant Pot. Ensure to coat oil & butter over whole bottom of the pot. Add chopped onions in Instant Pot. Lightly season with kosher salt and freshly ground black pepper. Saute for roughly 2 minutes until soften but not brown. Add in chopped garlic and saute until fragrant (~30 seconds). Add in about 16 broccoli florets and saute until it smells earthy (~90 seconds). Add in chopped carrots, 3 tbsp (45g) Jasmine rice, and 1 tsp ground mustard. Give it a few quick stirs.
Deglaze: Pour in ½ cup (125ml) unsalted chicken stock and completely deglaze bottom of the pot by scrubbing the flavorful brown bits with wooden spoon.
Pressure Cook Broccoli Soup: Add in remaining broccoli, 2 tbsp (30ml) fish sauce, and 2 ½ cup (625ml) unsalted chicken stock. Close lid and pressure cook at High Pressure for 3 minutes + 10 minutes Quick Release (after pressure cooker has finished cooking, wait 10 minutes then carefully release the remaining pressure). Turn off the heat. Open the lid carefully.
Grate Cheddar Cheese: While the soup is pressure cooking, freshly grate the cheddar cheese.
Blend & Create Broccoli Soup: In a bowl, reserve 16 - 18 broccoli florets. Pour in 2 cups (500ml) whole milk to slightly cool down the broccoli soup. Blend broccoli soup into a smooth consistency with an immersion hand blender. *Optional: Strain the broccoli soup over a fine mesh strainer for maximum smoothness.
Add in Cheddar Cheese: With a wooden spoon, add a handful of grated cheddar cheese at a time and stir constantly until the cheese fully melts. Taste and adjust accordingly as you may not need all the cheddar cheese. Add in the reserved broccoli florets and break them down a little with wooden spoon. Taste the soup and season with salt & ground black pepper.
Serve: Enjoy immediately. Just like our Creamy Tomato Basil Soup Recipe, this will be a really good soup to serve to your favorite guests with grilled cheese sandwiches on the side.