Martha says of this simple brunch dish of fluffy French toast stuffed with pears, "filling it with fruit may be an idea Mom borrowed from me, which is kind of nice—the learning going in the other direction."
Melt 1 tablespoon butter in a large skillet over medium-high heat. Add pear slices and 1 tablespoon sugar; cook, stirring occasionally, until pears are tender and caramelized, about 10 minutes.
Put eggs, milk, orange juice, eau de vie, if desired, lemon juice, remaining 2 tablespoons sugar, salt, and zests in a wide, deep dish. Beat well with a fork.
Dip brioche slices into egg mixture; transfer to a rimmed baking sheet. Divide pears among half the slices. Top with remaining slices.
Melt remaining 3 tablespoons butter in a large nonstick skillet over medium heat. Transfer 2 or 3 pear sandwiches to skillet with a spatula. Cook until deep golden brown on one side, about 2 minutes. Turn; cook until deep golden brown and slightly puffy all over, about 2 minutes more. Repeat with remaining sandwiches. Serve immediately with maple syrup or confectioners' sugar, if desired.