summer squash white bean soup

Ingredients

• 2 tablespoons butter
• 2 tablespoons olive oil
• 2 large sweet onions, chopped (about 4 cups)
• 2 garlic cloves, minced
• 4 medium yellow summer squash, cubed (about 6 cups)
• 1 carton (32 ounces) chicken broth
• 2 cans (15 ounces each) cannellini beans, rinsed and drained, divided
• 1/4 cup minced fresh parsley
• 1 to 2 tablespoons minced fresh tarragon
• 3/4 teaspoon salt
• 3/4 cup plain Greek yogurt