Bring 6 cups water to a boil in a 4-quart pot over high heat. Add 1 tsp. salt, then add the cauliflower and boil until very tender, 10 to 12 minutes. Drain the cauliflower in a colander set over a large bowl to catch the cooking liquid and let the cauliflower cool slightly.
Working in 2 batches, purée each batch of cauliflower with 2 cups of the cooking liquid and 2 Tbs. of the butter in a blender until very smooth. Season to taste with salt. (The soup can be made up to 4 hours ahead.)
In a small bowl, combine the almonds, peppers, oil, mint, garlic, and pepper flakes Season to taste with salt and pepper. (The relish can be made up to 1 hour ahead.)
When ready to serve, gently reheat the soup over medium-low heat. Garnish each serving with a spoonful of the almond relish.
nutrition information (per serving):
Photo: Christopher Hirsheimer; food styling by Melissa Hamilton