This soup started with the desire to make potato leek soup, but all I had on hand were sweet potatoes. It could very easily be vegan if you replaced the butter with a vegetable-based cooking fat (but man, do I love me some butter). —michael wilsker
large leeks, cleaned and trimmed, halved, and sliced into 1/2" pieces.
sweet potatoes. peeled, cut into approx. 1/2" cubes
In a heavy pot (I used a cast iron dutch oven), heat the butter over medium high heat until it melts and then bubbles. Add the olive oil and allow it to heat for approximately 10-15 seconds.
Once the oil has heated, add the leeks and stir to coat with the butter/oil mixture. Stir in the salt. Saute the leeks, stirring occasionally until they're soft but not browning, approx. 10 minutes.
Add the potatoes, the stock, the coconut milk, the basil and the bay leaf, stir, and bring to a boil. Once boiling, reduce heat and allow to simmer until the potatoes are cooked through, about 15 minutes.
Remove the bay leaf. (it's much harder to do this step after you've blended the soup.)
Once potatoes are cooked through, reduce heat to low, and, using an immersion blender, puree the soup until it's mostly smooth but with a slightly chunky texture.
Continue simmering over medium heat until the soup thickens to your liking, at least 10 minutes is recommended (mine took about 30).
Season with salt and fresh ground pepper to taste.
Serve at your leisure. It goes well underneath a dollop of greek yogurt and finely chopped green onions.