For orange syrup:
3/4 cup granulated sugar
1/2 cup water
1 vanilla bean
1/4 cup fresh orange juice
For almond cream:
1/2 cup natural almonds (2 1/2 ounces)
1/4 cup granulated sugar
1/4 cup almond paste (not marzipan; 2 ounces), cut into pieces
5 tablespoons unsalted butter, softened
1 large egg
1 tablespoon rum
1/2 teaspoon pure almond extract
8 (day-old) croissants
good quality chocolate pieces
3/4 cup sliced natural almonds (3 ounces), toasted
Confectioners sugar for dusting
Special equipment: a pastry brush, parchment paper
Combine sugar and water in a small saucepan. Split vanilla bean with a sharp small knife and scrape seeds into sugar mixture. Add pod and bring to a boil, stirring until sugar is dissolved. Simmer 1 minute, then remove from heat and stir in orange juice.
Make almond cream:
Pulse almonds with 2 tablespoons sugar in a food processor until finely ground. Add almond paste and pulse until finely chopped.
Beat together butter, remaining 2 tablespoons sugar, almond mixture, and a pinch of salt with an electric mixer at medium speed until fluffy, 2 to 3 minutes. Whisk together egg, rum, and extract in a small bowl and gradually add to almond cream, beating until combined well. Chill, covered, until set, about 1 hour.
Preheat oven to 350°F.
Cut croissants in half horizontally. Brush insides of croissants (both top and bottom halves) with some orange syrup. Spread 2 tablespoons almond cream on each bottom half, mounding in centers, top with chocolate and cover with tops. Spread 1 tablespoon almond cream on each top. Transfer croissants to a parchment-lined baking sheet and sprinkle about 2 tablespoons toasted almonds on each.
Bake croissants in middle of oven until golden brown, 20 to 25 minutes. Cool slightly, then dust with confectioners sugar.