Preheat your oven to 180C | 350F; line a 12-cup non-stick muffin tray with muffin liners OR spray with cooking oil spray; wipe over excess and set aside.
For Muffins:
Combine cream cheese, 1 teaspoon sugar and lemon juice in a small bowl; mix to combine.
Spread cream cheese mixture over 1 side of each slice of bread. Sandwich two slices together at a time and cut each sandwich into 1-inch cubes. (You should end up with 8 cups of cubed bread).
Whisk the eggs, milk, 1/4 cup of sugar, salt (if using) and vanilla together in a large shallow dish. Add the bread and mix it through the egg wash (using your hands is easier than a spoon), until all bread is thoroughly soaked. Drizzle extra lemon juice over the top (optional), and gently fold through the blueberries. Using a spoon, fill the muffin cups with the french toast mix (about 3 tablespoons per muffin hole). Set aside and make your streusel:
To make Streusel:
Combine the sugar and flour in a small bowl; cut in butter using a metal fork until crumbly. Sprinkle over muffins. Top with extra blueberries.
Bake muffins 20-30 minutes, or until streusel on top has turned golden in colour. Allow the muffins to cool in the pan 5 minutes, or they may fall apart when taken out too soon.
Serve straight away with maple syrup.
Notes
These can also be served with ice cream, frozen yogurt or extra fresh blueberries. Alternatively, store them in the refrigerator for up to 3 days, or the freezer for up to 2 weeks. Reheat in the oven when needed following instructions above. (Microwaving the muffins to reheat them creates a soggier muffin rather than the crispy freshly baked muffin and is not recommended).