Broccoli and Cheddar Twice-Baked Potatoes
4 medium russet potatoes, washed well and dried, 1 teaspoon olive oil, 3 and 1/2 tablespoons salted butter, very soft, 1/2 cup non-fat Greek yogurt, 1/4 cup buttermilk, 1/2 teaspoon salt, 1/2 teaspoon pepper, 3/4 teaspoon chives