- 3 russet potatoes (about 2 pounds)
- 2 cups very small broccoli florets, if desired
- 1 cup water for steaming
- 3 TBS unsalted butter (I only buy salted so just decrease the amount of salt you add to the soup)
- 1/2 medium onion, chopped (about 1/2 cup)
- 1 TBS flour
- 1 tsp. mustard powder
- 1 cup milk
- 2 cups vegetable stock (I never have vegetable stock so would use chicken stock)
- 1/2 cup heavy whipping cream
- 1 tsp. kosher salt, plush more to taste (less if using salted butter)
- 1/4 tsp. freshly ground black pepper
- 1/4 cup sour cream, for garnish
- 3 TBS minced fresh chives, for garnish
- 2/3 cup shredded sharp Cheddar Cheese, for garnish
- Prepare potatoes. Peel the potatoes. Chop one into 1/2-inch cubes and the other 2 into 1- to 2- inch chunks. Set aside larger chunks.
- Pressure cook the potatoes and broccoli. Put the small (1/2-inch) potato cubes and the broccoli into a steamer basket. Pour the water into the Instant Pot and place the steamer basket inside. Lock lid into place. Select Manual; adjust the pressure to high and the time to 0 minutes. After the pot beeps, quick release the pressure. Unlock and remove the lid. Use tongs or a potholder to remove the steamer basket. Set aside.
- Prepare the soup. Pour the water out of the pot. Preheat the Instant Pot by selecting Saute and adjust to Normal for medium heat. Put the butter in the pot to melt. When it has stopped foaming, add the onion and cook, stirring frequently, until the onion pieces have separated and begun to soften, 2 to 3 minutes. Add the flour and mustard powder and stir to coat onions. Cook, stirring frequently, until the flour has darkened slightly, about 2 minutes. Add milk and stir. Bring the liquid to a simmer and cook until milk is smooth and thickened, about 3 minutes. Add the stock, cream, large potato chunks, and salt. Stir to combine.
- Pressure cook the soup. Lock the lid in place. Select Manual; adjust pressure to High and the time to 8 minutes. After cooking, naturally release the pressure for 10 minutes, then quick release any remaining pressure. Unlock and remove lid.
- Finish the soup. Use a potato masher to break up the potatoes and thicken the soup. Add cooked potatoes and broccoli and let them simmer until warmed through. (Test a piece of potato first; if it’s not quite done, add the potatoes to simmer for a couple minutes before adding the broccoli.) Season with the black pepper and additional salt if necessary. Ladle into bowls, garnish with the sour cream, chives, and cheese, and serve.
COOKING TIP: Steaming some of the potatoes separately (as you’ll do in step 2) yields discrete pieces of potato, while the rest melt into the soup to thicken it. If you prefer, you can cook all the potatoes in the soup at once.