Most broccoli soup recipes don’t exactly scream “vibrant” or “verdant.” In fact, I’d wager that most people are more familiar with cream of broccoli soup, or its cheesier cousin, broccoli cheddar soup. This soup subverts all of those expectations: A luscious, bright green broth that’s just as rich and velvety (but without the dairy), dotted with perfect morsels of charred broccoli, melted leeks, and crisp-tender snap peas. It’s particularly well suited to the “shoulder” seasons—the periods after summer or before spring, when temperatures are neither too hot or too cold, but perfect for green crops like spring onions, peas, and of course broccoli.
But making a perfectly smooth broccoli soup without relying on dairy can be tricky. Fibrous broccoli with its multitude of textures is a challenging ingredient for pureed soups. For a silky, creamy texture, it’s important to cook broccoli thoroughly, until it’s soft and broken down; unfortunately, broccoli cooked to this degree often loses its bright green color as chlorophyll breaks down over time and exposure to heat, turning pale and unappetizing. So how do we get a creamy texture while keeping that attractive green color? We leverage the power of pH.
Seeing Green: How Baking Soda Enhances the Soup
I’ve written at length in my article on how pH can affect vegetable cooking. Baking soda acts as a weak base when dissolved in water, raising the pH of the water. When blanching water has a higher pH value (around 8.5), chlorophyll degradation slows, retaining more of the green hue in vegetables like broccoli. Additionally, sodium bicarbonate in particular reacts with chlorophyll to form chlorophyllin, a bright green salt derivative of chlorophyll. (Chlorophyllin is produced by removing a magnesium ion from the chlorophyll molecule and replacing it with sodium. This small substitution makes chlorophyllin more stable than chlorophyll. And more stable means more green.)
But adding baking soda to blanching water can be a double-edged sword: Yes, it can help retain the green color in chlorophyll-rich vegetables. But it also tends to lead to mushy textures. Why? In a high-pH cooking environment (say, greater than 8.0), pectin (the polysaccharide found in the cell walls of all land plants) breaks down and dissolves more quickly, leading to mushier, softer textures as the cell walls fall apart more readily.
In general, that mushiness can be a bad thing. But for the purposes of pureeing to make a soup, mushiness is perfect! The resulting puree is velvety, smooth, without a hint of fibrousness. And because adding baking soda to the cooking water enhances that rapid breakdown of pectin, this also reduces the cooking time dramatically—shaving off a few minutes from the ten minutes otherwise required in neutral pH water without added baking soda.
Once the green puree is properly blended and mixed back into the final soup, it’s important to heat the soup until just warmed through and to then remove it from heat. This will preserve the soup’s vibrant green color.
Even More Green: Build Flavor with Even More Green Vegetables
While broccoli is plenty rich in chlorophyll, it can be a bit overpowering and one-dimensional in its sulfurous flavor. To temper that flavor, I add even more chlorophyll to the mix by blanching green leek tops and parsley in the same pot before blending it all together with the broccoli. In addition to vibrant color, this intensely green puree also provides most of the soup’s body and texture.
Finishing Touches
At this point, there’s plenty of vegetal flavor in the puree. But to bring richness and depth, I build a brothy base with leek whites, garlic, fish sauce, and a sneaky spoonful of bouillon paste. These sources of umami lend a meatiness to the soup, without adding much meat (if any at all). For textural contrast, I char extra broccoli florets to serve in the soup, and fold in snap peas at the very end for a welcome crisp-tender crunch. The finished soup is savory, velvety, unctuous, and above all, visually striking. It’s also probably got enough servings of green vegetables for an entire week—which is always a plus.
In a Dutch oven, stir together 3 quarts water, 1 tablespoon (9g) salt, and baking soda until evenly distributed. Bring liquid to boil over high heat. Add the 2-inch pieces broccoli (8 ounces) to pot and cook until vibrant green and a knife pierces easily into the stem, 5 to 6 minutes. Use a spider skimmer or large slotted spoon to remove and set aside. Return water to a boil and add sliced dark green leek tops and parsley and cook until vibrant green and wilted, 1 to 2 minutes longer. In a fine-mesh strainer or colander, drain vegetables and discard water.
Transfer the blanched broccoli, leek tops, and parsley to the jar of a blender. Add 2 cups (475ml) cold water and blend on high speed, scraping down sides as needed, until smooth, 30 to 60 seconds. Set aside.
Wipe the now-empty Dutch oven dry with a clean kitchen towel. In the dry Dutch oven, heat 3 tablespoons (45ml) oil over high heat until shimmering. Add remaining 1-inch broccoli florets (8 ounces) in a single layer and cook until the first side is roasted and well browned, 4 to 6 minutes. Carefully flip broccoli and cook until the second side is roasted and well browned, about 4 to 6 minutes longer. Transfer charred broccoli to a plate and season with salt to taste. Set aside.
In now-empty Dutch oven, heat remaining 3 tablespoons (45ml) oil and pepper over medium-low heat until pepper begins to sizzle, about 30 seconds. Add white and light green leek slices and remaining 1 teaspoon (3g) salt and cook, stirring occasionally, until vegetables soften, about 3 minutes. Stir in garlic and bouillon paste and cook until fragrant, about 30 seconds. Stir in fish sauce and cook until slightly evaporated, about 15 seconds. Stir in remaining 2 cups (475ml) water and bring mixture to a simmer. Add the reserved green broccoli puree and stir until combined. Cook soup until heated through, about 1 minute.
Off heat, stir in snap peas. Season with salt and pepper to taste. Ladle soup into individual bowls and portion charred broccoli florets on top. Drizzle with olive oil and lemon juice or vinegar (if desired). Serve.
Special Equipment
Dutch oven, high speed blender, colander
Notes
If you don’t prefer chicken bouillon paste, you can double the amount of fish sauce in the recipe.
Make-Ahead and Storage
The broccoli puree base can be refrigerated for up to 2 days. When ready to serve, proceed with step 3 to finish.
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