Pistachio-Chai Muffins

INGREDIENTS

• 7.9 ounces all-purpose flour (about 1 3/4 cups)
• 1/2 cup packed brown sugar
• 1 teaspoon baking powder
• 1 teaspoon baking soda
• 1/4 teaspoon salt
• 2 chai blend tea bags, opened
• 1 cup low-fat buttermilk
• 1/4 cup butter, melted
• 1 1/2 teaspoons vanilla extract, divided
• 1 large egg, lightly beaten
• Cooking spray
• 1/3 cup shelled dry-roasted pistachios, chopped
• 1/2 cup powdered sugar
• 1 tablespoon water