I used yellow summer squash here, but you can certainly substitute any green summer squash/zucchini.
1 teaspoon cumin seeds
1/4 cup / 2 oz / 55g unsalted butter
fine grain sea salt
3 tablespoons unsalted butter
2 medium yellow onions, chopped
2 medium garlic cloves
1 pound / 16 oz / 450 g potatoes, cut into 1/4-inch cubes
2 1/2 pounds / 40 oz / 1+kg yellow summer squash, cut into 1/2-inch slices
4 cups / 950 ml good tasting vegetable stock
1 cup / 240 ml buttermilk
1 bunch of chives, chopped
In a skillet, over medium heat, toast the cumin seeds until they are fragrant. Just a minute or two. Use a mortar and pestle to pound the seeds into a fine powder. Alternately, you can use an electric spice grinder. Set aside. In the same skillet, melt the butter and cook until it’s brown and gives off a deliciously nutty aroma. Remove from heat, stir the cumin into the butter along with a generous couple pinches of salt, then set aside in a warm place. You want the butter to stay liquid until you’re ready to use it.
To make the soup, heat the butter in your largest pot or stockpot over medium-high heat. Add the onions, garlic, and a bit of salt. Saute for a few minutes, or until the onions start to get translucent. Stir in the potatoes and squash and cook for another 7-10 minutes, or until the squash starts to soften up. Stir in 3 1/2 cups of the stock (most of it) – the stock should just barely cover the vegetables. Bring to a boil. Reduce heat to a simmer and cook until the potatoes are tender, roughly another 25 minutes. Remove the soup from heat, puree completely with a hand blender, then stir in the buttermilk. If you need to thin the soup out with a bit more stock, you can do so. Taste and add more salt if needed. Serve each bowl topped with plenty of the cumin butter, and a sprinkling of chives.