Most permutations of cauliflower (roasted florets, cauliflower rice, yes, even cauliflower gnocchi) rarely tempt me. But when you simmer a whole head of cauliflower with onion, garlic, and half-and-half, then blend it all until thick and velvety, it makes a sublime creamy cauliflower soup that’s all the more remarkable because it’s so quick to prepare. Half-and-half adds just the right amount of rich dairy flavor to help the cauliflower taste its best, but you could also use milk, heavy cream (or mix equal parts of both for DIY half-and-half), or plant-based milk. Don’t skip the white pepper or the fresh lemon juice—they’re the secret ingredients that’ll have you craving spoonful after spoonful. The cheesy mustard croutons on top offer an ideal mix of sharp and rich flavors, but this creamy soup would also be delicious topped with toasted sunflower seeds, a spoonful of chili crisp, or some pesto. —Christina Chaey
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3 Tbsp. extra-virgin olive oil, divided, plus more for drizzling
1 medium onion, chopped
1½ tsp. Diamond Crystal or ¾ tsp. Morton kosher salt, plus more
3 garlic cloves, finely chopped
1 large head of cauliflower (2½–3 lb.), florets broken into small pieces, core chopped
¼ tsp. freshly ground white or black pepper, plus more
¾ cup half-and-half
1 Tbsp. Dijon mustard
1 Tbsp. unsalted butter, melted
5 cups country-style bread, preferably day-old, torn or sliced into 1″ cubes
½ cup finely grated Gruyère or cheddar
1 Tbsp. plus 1½ tsp. fresh lemon juice
Place a rack in middle of oven; preheat to 350°. Heat 2 Tbsp. extra-virgin olive oil in a large saucepan or small Dutch oven over medium-low. Add 1 medium onion, chopped, and season with kosher salt. Cook, stirring occasionally and reducing heat if onion starts to brown, until softened but without taking on any color, 5–7 minutes. Add 3 garlic cloves, finely chopped, and cook, stirring, until softened and fragrant, about 2 minutes. Add 1 large head of cauliflower (2½–3 lb.), florets broken into small pieces, core chopped, 1½ tsp. Diamond Crystal or ¾ tsp. Morton kosher salt, ¼ tsp. freshly ground white or black pepper, and 5½ cups water (the water should just barely cover the cauliflower). Bring to a boil, then reduce heat, and simmer, uncovered, until cauliflower is completely tender and starting to fall apart, 15–20 minutes. Stir in ¾ cup half-and-half and simmer 5 minutes; remove from heat.
While the soup is simmering, whisk 1 Tbsp. Dijon mustard, 1 Tbsp. unsalted butter, melted, and 1 Tbsp. extra-virgin olive oil in a medium bowl to combine; season with salt and pepper. Add 5 cups country-style bread, preferably day-old, torn or sliced into 1″ cubes, and toss to coat in mustard mixture. Scatter ½ cup finely grated Gruyère or cheddar over and toss again to combine. Transfer bread mixture to a parchment-lined rimmed baking sheet and bake in a single layer, turning halfway through, until cheese is melted and croutons are golden brown and crisp, 10–15 minutes.
Working in batches, carefully purée soup in a blender until very smooth, transferring to a medium bowl as you go. (Alternatively, you can use an immersion blender to blend soup in pot until smooth.) Return soup to pot and reheat over medium-low, stirring and adding more water to thin if needed (you’re going for the consistency of heavy cream). Stir in 1 Tbsp. plus 1½ tsp. fresh lemon juice. Taste and season soup with more salt and/or pepper if desired.
Ladle soup into bowls. Top with cheesy mustard croutons and drizzle with more oil.
Do ahead: Soup can be made 3 days ahead. Let cool; cover and chill. Reheat soup over medium-low, adding a splash of water to thin if needed.
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