6 ears corn, husks and silks removed
1 1/2 quarts chicken or vegetable stock
1 bay leaf
1 teaspoon whole fennel seed
1 teaspoon coriander seed
1 teaspoon whole black peppercorns
1 medium onion, finely diced (about 1 cup)
2 medium cloves garlic, minced
3 tablespoons flour
1 to 2 russet potatoes, peeled and cut into 1/2-inch dice (about 1 1/2 cups diced potato)
2 cups half and half or milk
Kosher salt and freshly ground black pepper
3 green onions, finely sliced
Hold one corn cob upright in a large bowl and cut off kernels with a sharp knife. Repeat with remaining cobs and reserve kernels and cobs separately.
Use the back of a knife to scrape corn cobs into a medium saucepan to collect and milk left in the bases of the kernels. Break corn cobs in half and add to saucepan. Add chicken or vegetable stock, bay leaf, fennel seed, coriander seed, and whole black peppercorns. Stir to combine. Bring to a boil over high heat, reduce to just below a simmer, and let steep for 10 minutes. Strain through a fine mesh strainer and discard cobs and spices.
While stock infuses, melt butter in a separate 3 quart saucepan over medium-high heat. Add onions, garlic, and corn kernels, and cook, stirring frequently, until onions are softened and kernels are tender, about 7 minutes. Reduce heat if butter begins to brown. Add flour and cook, stirring constantly, for 1 minute.
Stirring constantly, gradually add infused corn stock, letting mixture come to a simmer. Add potatoes. Let simmer, stirring occasionally, until potatoes are tender, about 10 minutes. Add half and half and stir to combine. Soup may look broken with melted butter floating on top at this stage.
Transfer 1/4 of soup to a blender and blend on high heat until smooth, about 1 minute. Return to pot and whisk to combine. Alternatively, use a hand blender to blend in the pot until desired consistency is reached. Season to taste with salt, pepper. Serve immediately, sprinkled with sliced scallions.
Makes about 3 quarts, serving 6 to 8.