Butter a 13 by 9-inch baking dish. Cut twenty 1-inch slices, on the bias, from baguette and arrange in one layer in baking dish.
In a large bowl whisk together eggs, milk, nutmeg, vanilla, and 3/4 cup brown sugar and pour evenly over bread. Chill mixture, covered, until all liquid is absorbed by bread, at least 8 hours, and up to 1 day.
Preheat oven to 350 degrees F.
In a shallow baking pan spread pecans evenly and toast in middle of oven until fragrant, about 8 minutes. Toss pecans in pan with 1 teaspoon butter and salt.
Increase temperature to 400 degrees F.
Sprinkle pecans and blueberries evenly over bread mixture. Cut 2 ounces (1/2 stick) butter into pieces and in a small saucepan heat with remaining 1/4 cup brown sugar, stirring, until butter is melted. Drizzle butter mixture over bread and bake mixture 20 minutes, or until any liquid from blueberries is bubbling.
In a small saucepan cook blueberries and maple syrup over moderate heat until berries have burst, about 3 minutes. Pour syrup through a sieve into a heatproof pitcher, pressing on solids, and stir in lemon juice. Syrup may be made 1 day ahead and chilled, covered. Reheat syrup before serving.