Step 1

Chop chocolate into small pieces with a knife or a food processor. The smaller the pieces, the more evenly the chocolate will melt.In a double boiler, whisk together the milk, sugar, and salt. Heat the milk over medium heat (not high!), whisking frequently, till hot but not boiling.

Step 2

Add the chocolate to the milk and let it sit for 1 minute in the heated milk without touching. Gently stir with a spatula till the chocolate melts into the milk. Remove from heat and continue stirring slowly till the milk and chocolate mixture is smooth and no longer grainy. If there are a few solid pieces of chocolate that refuse to melt, you can use an immersion blender to break up those pieces. Stir again with the spatula after blending to break up any air bubbles.

Step 3

Drain off any excess liquid from Greek yogurt before measuring 2 cups into a medium mixing bowl. Use a fork to whip the yogurt till fluffy.

Step 4

Stir the chocolate mixture again, then pour it into the yogurt, using a spatula to scrape up any remaining chocolate. Add the optional liqueur, if desired. Use spatula to fold the chocolate into the yogurt till fully incorporated, light and creamy. This will take 2-3 minutes. Continue folding till all the white has been removed from the yogurt.

Step 5

Divide the mixture between 6 ramekins, dessert bowls or mugs. Smooth and swirl the top of each serving with a spoon. Chill for at least 2 hours, up to overnight. Serve cold.