Preheat the oven to 180°C (350°F) and lightly grease an 11 x 9 inch (28 x 23 cm) baking tray with butter.
In a large bowl, combine the oats, flour, baking powder, cacao powder, sea salt, and raspberries and mix well.
Whisk together the milk, maple syrup, vanilla, and eggs in a separate bowl and then pour this mixture over the dry ingredients.
Stir to coat the dry ingredients thoroughly with the wet ingredients.
Tip the mixture into the prepared baking tray and smooth to the edges. Bake for 20-23 minutes, or until the top looks lightly browned and a toothpick comes out mostly clean.
Allow the baked oatmeal to sit for 5-8 minutes before serving with a side of freshly whipped cream or yogurt and seasonal fruit.