Ingredients:

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Instructions:

  1. Preheat oven to 400°F (200°C). Line a standard 12-cup muffin tin with paper liners or grease thoroughly.
  2. In a large bowl, whisk together the flour, sugar, baking powder, and salt for the vanilla batter.
  3. In a separate medium bowl, lightly whisk the egg, milk, oil, and vanilla extract until just combined.
  4. Pour the wet ingredients into the dry ingredients. Use a spatula to mix only until just moistened. A few streaks of flour are acceptable; do not overmix.
  5. In a small bowl, whisk the sifted cocoa powder and boiling water (or coffee) together until smooth and glossy to create the chocolate portion.
  6. Scoop approximately two-thirds of the main vanilla batter into a separate, clean bowl.
  7. Gently fold the cocoa mixture into the smaller portion of vanilla batter until it is mostly combined, creating the chocolate batter.
  8. Alternate large scoops of the vanilla batter and the chocolate batter into the prepared muffin cups, filling each liner about ¾ full.
  9. Insert a butter knife or small skewer into the centre of each filled cup and gently swirl 1-2 times to create the marble effect. Do not over-agitate the batter.
  10. Bake for 5 minutes at 400°F (200°C). Immediately reduce the oven temperature to 375°F (190°C) and continue baking for an additional 15–18 minutes, or until a skewer inserted comes out clean.
  11. Let muffins cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.