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

Melt the dark chocolate in a microwave-safe bowl in 30-second intervals until smooth. Set aside to cool.

In a mixing bowl, combine flour, baking powder, and salt, whisking to eliminate lumps.

In another bowl, whisk together sugar and eggs until pale and fluffy, then add cream cheese, yogurt, vegetable oil, and vanilla.

Fold the wet ingredients into the dry mixture until just combined.

Pour melted dark chocolate over the batter and gently swirl to create a marbled effect.

Fill muffin liners about two-thirds full with the batter.

Bake in the preheated oven for 18-20 minutes or until a toothpick comes out clean.

Cool for about 5 minutes, then transfer muffins to a wire rack to cool completely.