In a heavy-bottom saucepan, gently heat 2 cups of whole milk over medium-low heat. Stir occasionally until tiny bubbles form around the edges, about 5-7 minutes. Be careful to prevent curdling, then remove from heat.

Finely chop 200 g of dark chocolate into even pieces. This will help it melt smoothly when added to the hot milk.

Gradually whisk the chopped dark chocolate into the hot milk using a gentle figure-8 motion until smooth, which should take about 2-3 minutes.

Return the mixture to low heat, adding ½ cup of heavy cream, 1 teaspoon of vanilla extract, and a pinch of sea salt. Whisk until steaming but not boiling, about 3-5 minutes.

Warm serving cups with hot water, then pour the hot chocolate into each cup. Garnish with whipped cream or chocolate shavings if desired.