How to Make It
In a small saucepan, bring the milk just to a boil with the espresso beans. Remove from the heat, cover and let stand for 15 minutes. Strain the milk into a measuring cup; you should have about 5 ounces.
Wipe out the saucepan, return the milk to it and bring just to a simmer. Off the heat, stir in the chopped chocolate until melted. Whisk the sauce until smooth and transfer to a bowl. Keep warm.
In a medium saucepan, combine the 1 teaspoon of sugar with the butter, salt and 1 cup of water and bring to a boil. Off the heat, add the flour all at once and stir until incorporated. Scrape the mixture into a bowl. Using an electric mixer at medium speed, beat in the eggs one at a time until smooth. Add the vanilla and citrus zests. Scrape the batter into a pastry bag fitted with a 1/2-inch star tip.
In a medium bowl, combine the remaining 1 cup of sugar with the cinnamon and cardamom. In a large saucepan, heat 2 inches of vegetable oil to 350°. Working carefully and quickly, pipe about eight 3-inch lengths of batter into the hot oil; use a knife to cut between the pieces. Fry over moderate heat, turning once, until golden and cooked through, 5 to 6 minutes. Using a slotted spoon, lift out the churros and let drain for 10 seconds, then transfer them to the spiced sugar and toss to coat. Transfer the churros to a platter and keep warm. Repeat with the remaining batter and spiced sugar. Serve the churros with the mocha sauce.
The mocha sauce can be refrigerated for up to 1 week.