Prepare the coffee: Brew a strong cup of coffee, or dissolve 1-2 tablespoons of instant coffee in hot water. Let it cool slightly.
Melt the chocolate: In a double boiler or microwave-safe bowl, melt the sugar-free dark chocolate.If using a microwave, heat in 15-second intervals, stirring in between until fully melted and smooth. Mix the coffee and cream: In a separate bowl, whisk together the heavy cream, brewed coffee, sweetener, vanilla extract (if using), and salt. Stir until the sweetener is dissolved and the mixture is smooth.
Combine the chocolate and coffee mixture: Slowly pour the coffee-cream mixture into the melted chocolate, stirring gently until fully combined. The mixture should be smooth, glossy, and thickened.
Chill the mixture: Transfer the chocolate mixture to the fridge and let it chill for 30–45 minutes, or until firm enough to scoop.
Shape the truffles: Once the mixture has firmed up, use a spoon or melon baller to scoop out small portions and roll them into balls using your hands.
Coat the truffles: Roll each truffle in unsweetened cocoa powder to coat. For added texture, you can also roll them in finely chopped nuts or shredded coconut.
Chill again: Place the coated truffles on a parchment-lined baking sheet or plate and return them to the fridge for an additional 30 minutes to fully set.
Serve and enjoy: Let the truffles sit at room temperature for a few minutes before serving to get the ideal texture.