Preheat oven to 180°C (350°F). Line a muffin tin with paper liners.

In a bowl, mix flour, cocoa powder, baking powder, baking soda, and salt.

In another bowl, whisk sugar, eggs, yogurt, oil, and vanilla until smooth.

Combine wet and dry ingredients, mixing until just combined.

Fold in toasted walnuts gently.

Divide batter into muffin cups and bake for 18-20 minutes.

Cool on a wire rack before serving.