Grease 26 x 20 cm (10 x 8 or 9 x 9 inch) baking pan with butter.
Cut bread slices into 2 cm (1 inch) cubes ( I like to cut out crust).
Spread half of the bread cubes on the bottom of the pan. Press gently with your palm to squeeze bread pieces a bit.
In a small bowl beat 1 egg, add sour cream, sugar, vanilla, and lemon zest and mix until smooth.
Pour mixture over prepared bread. Spread half of the blueberries and cover everything with remaining bread cubes.
In another bowl beat 3 eggs, add milk, vanilla, cinnamon, and maple syrup. Pour mixture over bread, be sure to cover every piece of bread with mixture.
Spread the rest of blueberries on the top.
Wrap in foil and put in the refrigerator for at least 2 hours, preferably overnight.
When ready to bake, preheat oven to 180°C (350°F) and bake for 30-40 minutes, or until golden brown.
Serve warm.