How to Make It
Preheat the oven to 225°. In a medium stainless steel bowl, roast the chopped white chocolate for 3 hours, stirring every 15 minutes, until golden.
In a medium saucepan, bring the cream to a simmer over moderate heat. Remove from the heat, add the ground coffee and a pinch of salt and let steep for 2 minutes. Strain the cream through a fine sieve into the bowl with the roasted white chocolate and whisk until blended. Scrape the ganache into a shallow baking dish and press a piece of plastic wrap directly onto the surface. Refrigerate until firm, at least 3 hours.
Line a large rimmed baking sheet with parchment paper. Using a 1-inch ice cream scoop, drop heaping teaspoons of the ganache onto the prepared baking sheet. Moisten your hands with ice water and roll the ganache into balls. Refrigerate until very firm, about 1 hour.
Spoon the cocoa powder into a small bowl. In a medium bowl set over a saucepan of simmering water, melt the bittersweet chocolate over moderately low heat, about 3 to 5 minutes. Remove from the heat and stir the chocolate slowly until glossy and just starting to thicken, about 5 minutes.
Using a fork, dip each truffle in the melted chocolate, coat it in the cocoa powder, then return it to the baking sheet. Refrigerate the truffles to set the shells, about 15 minutes, before serving.