Melt the dark chocolate using a double boiler (bain-marie) or in the microwave, stirring at intervals until completely smooth and glossy.

In a bowl, whisk together the Greek yogurt, cocoa powder, honey (or maple syrup), vanilla extract, and salt until fully combined.

Gently fold the melted chocolate into the yogurt mixture using a spatula, mixing until smooth and evenly incorporated.

Divide the mousse into serving bowls and refrigerate for at least 1 hour, until set.

If desired, garnish with dark chocolate shavings or a dusting of cocoa powder just before serving.