01 - Preheat oven to 350°F. Grease a 2-quart ovenproof baking dish.
02 - In a large bowl, mix rinsed buckwheat, milk, water, maple syrup or honey, vanilla extract, cinnamon, and salt until well combined.
03 - Fold in mixed berries and diced apple if using, ensuring an even distribution.
04 - Pour the mixture into the prepared baking dish and spread evenly.
05 - Cover tightly with foil or lid and bake for 35 minutes.
06 - Remove cover, gently stir, then bake uncovered for an additional 10 minutes until the liquid is mostly absorbed and buckwheat is tender.
07 - Remove from oven, let rest for 5 minutes, then serve warm topped with additional berries, nuts, or a drizzle of maple syrup as desired.