Break the dark chocolate into small pieces and place in a heat proof bowl along with the butter. Suspend the bowl over a pan of barely simmering water and leave to melt.
Carefully cut each of the mini crème eggs into half and arrange all over the top of the brownie mixture, cut side up.
Bake in the centre of the oven for 35-45 minutes (35 for gooey brownies, 45 for more set ones).
Leave to cool completely in the tin before removing.
Melt the milk chocolate and white chocolate in separate bowls above pans of barely simmering water.
Divide the white chocolate in half, and colour one half with a few drops of yellow gel food colouring.
Pour the cooled, melted chocolate into piping bags and decorate the top of the cooled brownies.
Brownies will keep for several days in an airtight container.
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Notes
Cadbury Crème Eggs are not considered to be gluten-free as they are made in a factory that also handles wheat. However, their ingredients lists, in both the US and the UK contain no gluten-containing ingredients. It is important to read labels, check manufacturers websites, check ingredients and allergen lists, and make judgements based on your own judgement about your sensitivity and comfort levels.In 2016 Celiac.com added Cadbury Crème Eggs to their 'safe Easter candy list' for those following a gluten-free diet, but they do not recommend them for sensitive individuals. Visit Celiac.com for more information.