This French pastry is similar to French toast, only it's easier to pull off when feeding a crowd and offers a sweet, crisp surprise with its caramelized frangipane top crust. Martha made this recipe on Martha Bakes episode 605.
Preheat oven to 400 degrees and line baking sheet with parchment paper.
Make the simple syrup: In a small pot, combine sugar, 1/2 cup water, and vanilla bean; cook over medium-high heat, stirring, until sugar dissolves, about 2 minutes.
Make the frangipane: In bowl of a food processor, combine almonds and sugar and process until finely ground. Add butter, egg, flour, rum, salt, and almond extract, and process until frangipane is smooth.
Assemble the bostock: Slice brioche into eight 1-inch-thick slices. Brush both sides of each slice with simple syrup; place on prepared baking sheet. Spread each top evenly with 1 tablespoon jam and then 3 tablespoons frangipane.
Bake until golden brown, 13 to 15 minutes. Sprinkle with sliced almonds and dust with confectioners' sugar before serving.