**Prepare the chocolate**
Place the chopped dark chocolate in a heatproof mixing bowl and set aside.
**Heat the cream and milk**
In a medium saucepan, combine the heavy cream and milk. Heat over medium heat until just simmering, but do not let it boil.
**Whisk the yolks and sugar**
In a separate bowl, whisk the egg yolks and sugar together until smooth and pale.
**Temper the egg mixture**
Gradually pour a small amount of the hot cream mixture into the yolks while whisking constantly to prevent curdling. Slowly add the rest of the cream mixture while continuing to whisk.
**Cook the custard**
Pour the tempered mixture back into the saucepan. Cook over low heat, stirring constantly with a wooden spoon or heatproof spatula, until the mixture thickens enough to coat the back of the spoon (about 170–175°F or 75–80°C). Do not let it boil.
**Strain and mix with chocolate**
Strain the custard through a fine-mesh sieve into the bowl with the chopped chocolate. Let sit for 1–2 minutes to allow the chocolate to melt, then whisk until smooth and fully combined.
**Chill the crémeux**
Cover the surface of the chocolate crémeux with plastic wrap to prevent a skin from forming. Refrigerate for at least 4 hours or overnight until fully set.
**Serve**
Spoon the crémeux into serving dishes or ramekins. Garnish with whipped cream, berries, or chocolate shavings if desired.
