In a small saucepan, combine the blueberries, sugar and lemon juice, then set the heat to med-low. Let this simmer for 5-8 minutes, until the blueberries begin to release their juices and break down. While doing this, start preparing the French toast.

Place the butter into a small skillet over medium heat. In a shallow bowl, whisk together the egg, milk, cinnamon and vanilla. One at a time, dip each slice of bread into the egg mixture, flipping to coat both sides well. Once the butter has melted, place each bread slice into the skillet. Cook for 5 or so minutes, until golden. Then flip and cook until the opposite side is golden as well.