While other types of cinnamon and vanilla will do, des Jardins highly recommends seeking out Mexican vanilla, which has a creamy flavor with warm spice notes, and Mexican cinnamon, or canela, which is sweeter tasting and softer than cassia cinnamon.
Cook chiles and canela sticks in a large skillet over medium, turning occasionally, until lightly toasted and fragrant, about 4 minutes. Transfer chiles to a spice grinder; process until very finely ground, about 30 seconds. Reserve 3/4 teaspoon ground chiles for almonds; set remaining ground chiles and canela sticks aside.
Place chopped chocolate in a large heatproof bowl; set aside. Whisk together sugar, cocoa, xanthan gum, salt, and remaining ground chiles in a large saucepan. Add 4 cups water and canela sticks. Bring to a boil over medium, whisking occasionally. Boil 1 minute, whisking occasionally. Pour hot mixture through a fine wire-mesh strainer over chocolate; discard solids. Whisk until chocolate is melted and smooth. Whisk in vanilla extract.
Press plastic wrap directly on surface of sorbet base. Let cool at room temperature 1 hour. Transfer to refrigerator, and chill 8 hours or up to 24 hours.
Preheat oven to 350°F. Whisk together brown sugar, egg white, ground canela, and reserved 3/4 teaspoon ground chiles in a large bowl until well combined. Stir in almonds. Transfer mixture to a parchment paper–lined baking sheet, and spread into a single layer. Sprinkle with flaky sea salt. Bake in preheated oven until almonds are dry and toasted, 15 to 20 minutes, stirring once after 10 minutes. Let almonds cool completely; roughly chop, and set aside.
Transfer chilled sorbet base to freezer bowl of a 11/2-quart electric ice cream maker. Freeze according to manufacturer’s instructions until sorbet has the texture of soft serve, 50 minutes to 1 hour.
Quickly transfer sorbet to a freezer-safe container with lid; press parchment paper directly onto surface. Cover and freeze until firm, at least 6 hours. To serve, sprinkle with spiced almonds.
Almonds can be stored in an airtight container at room temperature up to 2 weeks. Sorbet can be frozen in an airtight container up to 3 months.