3 ounces 62% semisweet chocolate, chopped
3 ounces 70% bittersweet chocolate, chopped
1/2 cup heavy cream, preferably not ultrapasturized
1/4 cup cocoa powder
5 ounces 70% bittersweet chocolate, melted

Place the chopped chocolates in the top of a double boiler set over gently simmering water. Let the chocolate melt three-quarters of the way, then remove from the heat and stir until smooth. Return the pan to the bottom of the double boiler, off the heat, to keep warm.

Meanwhile, heat the cream in a small saucepan to between 115 and 120 degrees F. The goal is to have the chocolate and cream at the same temperature.

Slowly drizzle the melted chocolate into the cream, stirring with a heatproof spatula to blend and emulsify (this emulsification is called a ganache). Stir gently, do not overmix.

Pour the ganache onto a baking sheet and spread into a layer about 1/4 inch thick. Once it has reached room temperature, cover with plastic wrap and let it stand overnight at room temperature to solidify.

Scoop up a teaspoon of ganache on a spoon or with a melon baller and shape the chocolate gently into a ball. Place on a sheet of parchment paper. Do not roll the truffles in the palms of your hand at this point; it will compress them too much and make them hard. They don’t need to be regular in size or shape. Scrape up any remaining bits of ganache with a pastry scraper and form into truffles.

Place the cocoa powder in a small bowl. Place about a teaspoon of the melted chocolate in the palm of one hand, and roll a truffle between your palms to coat it lightly with chocolate. (Rolling the truffles between your hands at this point will create a very thin layer of chocolate that will prevent the cocoa from soaking into the truffle.) Roll the coated truffles in cocoa powder.

The truffles can be kept in an airtight container at room temperature for 2 days or refrigerated for up to 2 weeks. Allow the truffles to come to room temperature before serving. Makes about 3 dozen truffles.