Pre-heat your oven to 200C/180C Fan/Gas Mark 6. Line 6-7 muffin holes with cupcake/muffin liners.
In a small bowl, break up the dark chocolate and melt in the microwave in 20 second intervals, stirring in between to make sure it doesn't burn.
In a large mixing bowl, whisk together melted butter and both sugars. With an electric/stand mixer, go for a solid 3-5minutes so it is totally combined. Add in the eggs, one at a time and mixing in between.
Now, add the melted chocolate slowly (check it first, to make sure it isn't so hot that it will cook the eggs) and combine once again.
Add the flour and cocoa powder, fold gently until combined. Pour mixture into the lined muffin tins. This should easily fill about 6-7 - leave a little space at the top (1-2cm fine) as they will rise but shouldn't overflow!
Bake 20-25 minutes, until the tops look crisp/shiny. Whilst warm, use something round, like the end of a wooden spoon, to create the indentation that will act as the nest. The holes don't need to be too deep or wide. Let cool.
Once cool, add in the chocolate sauce and the mini eggs!
