Whisk together the eggs, milk and maple syrup in a large shallow bowl. Place a non-stick frying pan over a medium heat on the hob and then dunk two of the slices of bread in the egg mixture until they are completely covered. Leave them to sit for a couple of minutes, turning a few times to make sure the bread is fully soaked in the liquid. Transfer to the pan and fry for a couple of minutes until golden brown, then flip and fry for another couple of minutes on the other side. Transfer to a plate and cover with kitchen roll. Repeat with the remaining two slices.
To serve, top each slice with a dollop of mascarpone. Scatter over the blueberries then drizzle with the syrup.