In a separate bowl, lightly whisk the egg before adding the vegetable oil and milk. Whisk together until well combined. Pour the liquid ingredients into the well in the dry ingredients, and very gently fold the mixture together.
Use a teaspoon to make an indent in the centre of the mixture and add a heaped teaspoon of Biscoff spread. Add the remaining muffin batter to the top of the muffins.
Divide the Biscoff spread on to the top of the muffins and use a skewer or butter knife to gently swirl it around. Press half a Biscoff cookie into the top of each muffin to decorate.