Preparation

• In a metal bowl set over a saucepan of simmering water, melt the bittersweet and milk chocolate, stirring frequently with a rubber spatula to ensure even melting. In a small saucepan, heat the cream over medium heat to just below the boiling point.
• Remove the bowl of chocolate from the pan of water and wipe the bottom and sides dry. Pour the cream into the chocolate and stir with a spatula until very smooth. Stir in the hazelnut butter until well blended. Cover tightly with plastic wrap. Cool to room temperature, and then refrigerate until firm, about 3 hours, stirring occasionally with the spatula.
• With a small spoon or melon baller, scoop 3/4-inch balls of the chocolate mixture and roll them between your palms to round them off. Place the rolled truffles on a parchment-lined sheet tray.

• Sift the cocoa into a shallow bowl. Drop the truffles, a few at a time, into the bowl and shake and roll them in the cocoa until well coated. Transfer the truffles to a container with a tight-fitting lid, making sure they don’t touch each other. Refrigerate until ready to serve. Sealed, refrigerated truffles will keep for up to a week.