Simmer the heavy whipping cream and instant espresso powder in a medium saucepan set over medium heat. Small bubbles should begin forming along the edges of the pan without reaching a rapid boil.

Pull the pan from the heat, drop in the chopped unsweetened chocolate, and let the mixture stand undisturbed for 5 minutes. The resting period allows the gentle ambient warmth of the cream to melt the chocolate evenly.

Whisk in the powdered sweetener, butter pieces, and vanilla extract until completely glossy, then chill in the refrigerator for about 1 hour. The ganache is ready when it transforms from a liquid into a soft-matte, scoopable paste.

Portion the chilled ganache into 1-tablespoon mounds, roll them into smooth spheres, and arrange them on a wax-paper-lined cookie sheet before freezing for 1 hour. The frozen centers will feel firm to the touch and hold their shape during coating.

Melt the sugar-free dark chocolate chips and cocoa butter together in a heatproof bowl set over a pan of barely simmering water, stirring frequently until liquefied. The coating mixture should look completely glossy and pour easily from a spoon.

Drop each frozen truffle center into the melted chocolate, roll it quickly using two forks to coat the exterior, and lift it out while tapping the fork against the bowl rim. The excess chocolate drips away cleanly, leaving a thin, even layer on the wax paper.

Melt the white chocolate in a separate heatproof bowl set over the simmering water, stirring constantly until smooth. Transfer the melted confectionery into a small plastic bag with the very tip snipped for controlled drizzling.

Drizzle half the confections with remaining dark chocolate and decorate the rest with white chocolate, immediately topping each with an espresso bean before the shell sets. The cold interior will set the delicate outer coating within seconds.