01 - In a small mixing bowl, beat the softened cream cheese, granulated sugar, and vanilla extract together until completely smooth and creamy. Gently fold in the fresh blueberries, taking care not to crush them.
02 - Lay out all 8 slices of brioche on a clean work surface. Divide the cheesecake filling evenly among 4 slices, spreading it in a generous, even layer. Place the remaining 4 slices on top to form 4 stuffed sandwiches, pressing gently to seal.
03 - In a shallow dish or pie plate, whisk together the eggs, whole milk, ground cinnamon, and kosher salt until fully combined and smooth.
04 - Carefully dip each stuffed sandwich into the egg custard, allowing each side to soak for about 15 seconds. Ensure both sides and edges are evenly coated, then let any excess drip off.
05 - Melt the butter in a large nonstick skillet or griddle set over medium heat. Working in batches if needed, cook each sandwich for 3 to 4 minutes per side until deeply golden brown and heated through to the center.
06 - Transfer the cooked French toast to serving plates. Dust generously with powdered sugar and finish with additional fresh blueberries, a drizzle of maple syrup, or a dollop of whipped cream as desired.