Preheat your oven to 375°F (195°C) and line a standard muffin pan with paper liners.

Break the dark chocolate into small pieces and melt it in a microwave-safe bowl, stirring at 30-second intervals until smooth.

In a large bowl, whisk together flour, baking powder, and salt.

In another bowl, whisk sugar and eggs until pale and fluffy, then mix in cream cheese, Greek yogurt, vegetable oil, and vanilla until well blended.

Gently fold the wet mixture into the dry ingredients until just combined, ensuring the batter is slightly lumpy.

Pour the melted chocolate over the batter and swirl it in for a marbled effect.

Spoon the batter into the muffin tins, filling each cup about two-thirds full.

Bake for 18-20 minutes, checking for doneness with a toothpick.

Let the muffins cool in the pan for about 5 minutes before transferring them to a wire rack to cool completely.