Sieve the flour and cocoa powder into a bowl and add the sugar, stirring to mix.
Combine the eggs, sunflower oil, milk and vanilla extract in a jug, using a fork. Pour the wet ingredients into the dry and stir a few times until the ingredients are just combined.
Line a 12-hole muffin tin with paper cases. Half-fill the cases with muffin mixture, add 1 teaspoon chocolate spread to each case and then top with the rest of the muffin mixture.
Bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 25 minutes until the muffins are well risen and springy to the touch.