In a small saucepan, gently heat the heavy cream over medium heat until it begins to simmer. Take it off the heat and pour the hot cream over the finely chopped dark chocolate placed in a bowl. Let the mixture rest for about 2 minutes to soften the chocolate. Slowly stir the mixture until it becomes smooth and glossy. Incorporate the room-temperature butter, mixing until fully blended for a velvety consistency.

Cover the bowl with plastic wrap and refrigerate for 2–3 hours, allowing the mixture to firm up. Once ready, use a spoon or small ice cream scoop to portion out the mixture. Roll into balls or press into square shapes, as desired. Arrange them neatly on a tray lined with parchment paper. Chill the shaped truffles for an additional 30 minutes to ensure they set properly.

Melt the dipping chocolate in a heatproof bowl placed over a pot of gently simmering water, stirring occasionally to achieve a smooth, liquid consistency. Using a fork or dipping tool, immerse each truffle into the melted chocolate, ensuring it is fully coated. Allow any excess chocolate to drip off before placing the truffles back onto the parchment-lined tray.

While the chocolate coating is still soft, gently press a toasted cashew nut onto the top of each truffle. Let the truffles sit at room temperature or refrigerate briefly until the chocolate sets completely.

Arrange the finished truffles on a serving platter or package them in decorative wrappers for gifting. Relish these rich, cashew-topped chocolate delights as a dessert or a snack to brighten any occasion.