Pre-heat your oven to 160C Fan/180C/350F/Gas Mark 4 and grease and line a 12" x 9" traybake tin (check the recipe notes if you want to make in a 8" or 9" square tin)
Melt the dark chocolate and butter together in a pan on a low heat. When fully melted, stir together and remove from the heat. Let it cool for 10 minutes
In a mixing bowl use an electric mixer to whisk together the eggs, light brown sugar and vanilla extract for 5 minutes until thicker and paler in colour
Add the chocolate mixture to the egg mixture, whisking constantly as you pour it in
Add the plain flour and whisk in gently with a hand whisk until you can't see any more flour
Pour the batter into your lined tin. Bake for 15 minutes
While it is baking, cut the Creme Eggs in half. There will be one extra half - the perfect snack for the chef or a nearby child!
Take the brownies out of the oven, press the eggs into the batter, then put them back in the oven for 5-10 minutes. To check if they are done, insert a toothpick in the centre. It should come out with several crumbs on, but not be wet.
Let the brownies cool completely in the tin before removing and slicing up (this is important to make sure the brownies set!)
Store in an airtight container in a cool place and eat within 3 days