Birthday Cake Banana Bread

Ingredients

• 1/2 c. (1 stick) melted butter, plus more for pan -
• 1 c. all-purpose flour, plus more for pan -
• 1 tsp. baking soda -
• 1/4 tsp. kosher salt -
• 3/4 c. sugar -
• 1/4 c. buttermilk -
• 1 tsp. pure vanilla extract -
• 1 large egg -
• 1 large egg yolk -
• 3 super-ripe bananas, mashed with a fork -
• 1/2 c. white chocolate chips -
• 1/2 c. rainbow sprinkles -
• 1/2 c. powdered sugar -
• 1 tbsp. milk -
• 1/2 tsp. pure vanilla extract -