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1
Preheat oven to 375 F.
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2
Spread the cauliflower florets onto a large rimmed sheet tray that you've lined with parchment paper or a Silpat. Spray generously with olive oil spray. Combine salt, cumin and coriander in a small bowl, then sprinkle it over the cauliflower. Cut lemon into quarters, and add to the baking sheet too.
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3
Put pan into the oven. Roast for 20 minutes, until cauliflower is completely tender and golden brown in places.
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4
While the cauliflower is roasting, heat 2 tablespoons of the olive oil in a heavy-bottomed pot over medium heat. When oil is shimmering, add the sliced leeks, and cook, stirring from time to time, until leeks have softened and begin to caramelize. This will take about 10 minutes. Add garlic, and cook for another 2 minutes. Turn the heat down to low until the cauliflower comes out of the oven.
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5
When fully roasted, add the cauliflower into the leeks, then carefully squeeze in the juice from the roasted lemons (they will be hot so be careful). Stir to combine, then add the stock. Raise the heat to medium, and allow the soup to come to a gentle boil.
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6
Using an immersion blender, or working in batches with a regular blender, puree the soup completely. Add more stock as needed to thin to desired consistency. Lower heat to simmer again.
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7
To make the crispy capers: In a small skillet, heat 1/4 cup of olive oil over medium high heat. Drain capers, then carefully add them into the hot oil (they will sizzle and spatter so be careful). Fry, stirring from time to time, for about 3 minutes, until capers are beginning to crisp up. Transfer capers to a paper towel to drain.
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8
Add the oil from the capers into the soup, along with a splash of cognac. Stir one final time. Taste for seasoning, adding salt, pepper and more lemon juice as needed.
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9
To serve, ladle soup into bowls, add a healthy grating of Parmesan cheese (if using), and a handful of the fried capers.
