Step 1

Make the mustard seed butter: In a large pot over medium heat, toast the mustard seeds until they begin to release their aroma, shaking the pan a couple of times, about 1 minute. Reduce the heat to low and add the 2 tablespoons of butter. Cover and cook until butter melts and begins to sizzle, about 2 minutes. Transfer to a heatproof bowl, scraping the sides of the pot to get all of the mustard seeds. Stir in a pinch of salt and set aside.

Step 2

Make the soup: Return the pot to medium-low heat and add the 4 tablespoons of butter, the ginger, garlic and miso. Cook, stirring continuously, until the mixture turns into a golden paste, 2 to 3 minutes. It may stick to the bottom of the pot – that’s toasty goodness – but adjust the heat if it starts to burn.

Step 3

Add the wine, scraping the bottom of the pot, and reduce until the mixture coats the back of a spoon, about 2 minutes.

Step 4

Add the leeks, reduce the heat to low, cover and cook, stirring occasionally, until the leeks are soft, about 4 minutes.

Step 5

Add the potatoes, water and 1 teaspoon salt. Cover, increase the heat to high and bring to a boil. Reduce the heat so the soup is at a simmer, and cook until the potatoes are very tender, about 15 minutes.

Step 6

While the soup is simmering, in a medium bowl, toss the asparagus with the remaining 1/4 teaspoon of salt; set aside.

Step 7

Once the potatoes are cooked, turn off the heat. Add the asparagus and parmesan and stir well. Let the soup sit in the pot to melt the cheese and lightly cook the asparagus, about 1 minute.

Step 8

To serve, ladle the soup into individual bowls. Give the mustard seed butter a stir, then add 1/4 teaspoon of the butter, a squeeze of lemon, and sprinkling of fresh herbs to each bowl.