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 brioche slices on a clean work surface. Divide the cheesecake filling evenly among 4 slices, spreading it in a generous, even layer. Cap each filled slice with a remaining brioche slice to form 4 stuffed sandwiches, pressing gently to seal.
03 - In a wide, shallow dish, whisk together the eggs, whole milk, ground cinnamon, and salt until fully combined and slightly frothy.
04 - Submerge each stuffed sandwich into the egg custard, letting it soak for about 10 seconds per side. Ensure both sides are evenly coated but not oversaturated, allowing excess to drip off.
05 - Melt the butter in a large nonstick skillet or griddle set over medium heat. Once the butter is foaming, add the soaked sandwiches in batches if needed. Cook for 3 to 4 minutes on the first side until deep golden brown, then flip and cook another 3 to 4 minutes on the opposite side. The filling should be warm and the exterior crisp.
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. Serve immediately while hot.