Start by preheating your oven to 375°F. While it heats, lightly grease your baking dish with non-stick spray or a swipe of butter. This little step keeps the edges from sticking and makes cleanup painless once the bake is done.
Add the cottage cheese, eggs, milk, maple syrup, and vanilla extract into your blender. Blend until completely smooth, with no visible curds left behind. This is the step that gives the finished bake its custardy, cheesecake-like texture instead of a grainy one.
In a separate mixing bowl, stir together the rolled oats, baking powder, cinnamon, and salt. Getting the dry ingredients evenly combined first helps the baking powder distribute properly, so you don't end up with uneven pockets in the finished dish.
Pour the blended cottage cheese mixture into the bowl of oats and stir until everything is fully combined. The batter should look thick but pourable, similar to a loose cake batter. Don't overmix, or the texture can turn a bit gummy.
Gently fold most of your berries into the batter, saving a small handful to scatter on top. Folding instead of stirring hard keeps the berries whole so you get pretty pockets of fruit throughout instead of a purple-tinted batter.
Pour the batter into your prepared dish, smooth the top, and scatter the reserved berries over it. Bake for 30 to 35 minutes, until the top turns golden and the center feels set rather than jiggly when you gently shake the pan.
Let the baked oatmeal rest for about 5 minutes before slicing. This short rest lets it firm up so your pieces hold their shape instead of falling apart. Serve warm with your favorite toppings while the top is still slightly crisp.