16 ounces leeks – white and light green parts only, thinly sliced and rinsed
2 tbsp unsalted butter
16 ounces Yukon Gold potatoes – peeled and cut into 1-inch chunks
1.25 tsp kosher salt
1 sprig fresh thyme
1 leaf bay leaf
4.5 cups vegetable stock – low-sodium
0.25 tsp white pepper – ground
fresh chives – finely sliced (for serving)
Instructions
Trim, split lengthwise, and thinly slice the white and light green parts of the leeks; swish the slices in a bowl of cool water to remove grit, then lift out and drain well.
Melt the unsalted butter in a heavy pot over medium heat until foamy, 1–2 minutes.
Add the drained slices and cook, stirring often, until soft and sweet but not browned, 10–12 minutes.
Peel and cut the Yukon Gold potatoes into 1-inch chunks.
Stir in the kosher salt, then add the chunks, the fresh thyme, the bay leaf, and the vegetable stock; bring to a boil.
Reduce to a gentle simmer, cover partially, and cook until the chunks are very tender, 15–20 minutes.
Remove from heat, fish out the herbs, and discard.
Blend the soup until completely smooth using an immersion blender, or carefully in batches in a countertop blender; return to the pot and warm gently if needed.
Off heat, season with the white pepper.
Ladle into warm bowls and finish with fresh chives; serve hot.