Preheat the oven to 350°F and grease a 9x9-inch baking dish.
Add the cottage cheese, cream cheese, egg, sugar, lemon zest and vanilla extract to a blender. Blend until completely smooth and set aside.
In a large bowl, whisk the eggs, Greek yogurt, melted butter, sugar and vanilla until smooth. Add the flour, baking powder and salt and stir just until combined.
Spread half of the batter over the bottom of the baking dish. Pour the cottage cheese filling evenly over the top.
Dollop the remaining batter over the filling and gently spread it out. It does not need to cover the filling completely. Bake for 45 to 50 minutes, until puffed, golden and set in the center.
While the casserole bakes, stir the blueberries, maple syrup, lemon juice and cornstarch in a small saucepan. Simmer over medium heat for 5 to 7 minutes until the berries burst and the sauce thickens.
Let the casserole rest for 15 minutes before slicing. Serve warm with the blueberry sauce spooned over the top.