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1
Place the yogurt in a sieve lined with a paper towel.
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2
Set aside until all of the liquid has drained off, several hours or overnight in the refrigerator.
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3
Melt the butter in a large pot over medium heat.
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4
Add the onion and cook until soft, about 5 minutes.
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5
Add the broccoli stalks and florets and 3 cups of the chicken broth and bring to a boil.
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6
Reduce to a simmer, cover and cook until the broccoli is soft, about 20 minutes.
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7
Place half of the broccoli and cooking liquid with half of the yogurt in a blender.
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8
Hold the top down firmly with a kitchen towel and blend until coarsely pureed.
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9
Scrape the mixture into a large saucepan and repeat with the remaining broccoli, cooking liquid and yogurt.
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10
Stir in the remaining 1/2 cup chicken broth, the salt, pepper and cayenne.
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11
Warm the soup over low heat.
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12
Separate the broccoli rabe stems from the leaves.
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13
Cut the stems into 1/2-inch pieces and cut the leaves across into thin strips.
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14
Bring a medium-size pot of lightly salted water to a boil.
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15
Add the stems and blanch for 2 minutes.
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16
Remove with a slotted spoon.
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17
Add the leaves and blanch for 1 minute.
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18
Drain.
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19
Divide the soup among 4 bowls.
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20
Top with the broccoli rabe stems and then the leaves and serve immediately.