"Create a healthy white chocolate overnight oats recipe made in one container for 4 days, using only buttermilk and mixed frozen fruit as the dairy/fruit base. Include oats, chia seeds, milk, hot chocolate powder, and melted white chocolate. No yogurt. Make it suitable to prepare once and eat over 4 days from the same container. Use metric units. Include a rough method, storage guidance, and suggest any optional healthy add-ins if appropriate, but keep the recipe focused on the requested ingredients."