Step 1

Heat oil in a Dutch oven over medium-high. Add onion. Cook, stirring occasionally, until softened and translucent, 5 to 7 minutes. Add garlic, rosemary, salt, and pepper. Cook, stirring constantly, 1 minute. Add beans, broth, and bay leaf.

Step 2

Bring mixture to a boil over high. Reduce heat to low; simmer, stirring occasionally, 15 minutes. Remove and discard bay leaf.

Step 3

Add chard to Dutch oven. Cook over low, stirring occasionally, until chard is very tender and wilted, about 6 minutes.

Step 4

Working in 2 batches, ladle entire mixture into a blender. Secure lid on blender, and remove center piece to allow steam to escape. Place a clean towel over opening. Process until smooth, 2 to 3 minutes per batch. Return pureed soup to Dutch oven, and bring to a simmer over medium-high.

Step 5

Stir together sour cream and whole milk in a bowl. Top servings with sour cream mixture; garnish with chopped fresh chives and crushed red pepper.