Set your oven to 200°C (392°F) and allow it to fully preheat. Meanwhile, line a muffin tin with paper liners or lightly grease each cavity to prevent sticking.

In a large mixing bowl, sift the flour and baking powder together. This ensures even mixing and a lighter muffin texture.

To the bowl with the dry ingredients, add the Biscoff spread, chopped dark chocolate (if using), sugar, vanilla extract, milk, oil, and the egg. Using a spoon or spatula, mix the ingredients together vigorously until just combined. Be careful not to overmix—some lumps in the batter are fine, as overmixing can result in dense muffins.

Evenly divide the batter into the prepared muffin liners, filling each one about three-quarters of the way full. This allows room for the muffins to rise without overflowing.

Place the muffin tin in the oven and bake at 200°C (392°F) for the first 5 minutes. This initial high temperature helps create a nice dome on the muffins.

After 5 minutes, reduce the oven temperature to 170°C (338°F). Bake for an additional 20–25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.

Remove the muffins from the oven and let them cool in the tin for 5 minutes. Then transfer them to a wire rack to cool completely. Serve warm or at room temperature.