Preheat the oven to 180 degrees C and grease and line your baking tin.
Break the white chocolate up and place into a heatproof bowl and add in the butter.
Place in the microwave in 20 second increments, stirring between each one until melted. Make sure you mix it well between each heating in the microwave as chocolate can keep its shape, but actually be melted. Alternatively you can set the bowl over a small saucepan of simmering water and stir until melted.
Place the flour, baking powder, salt and mini eggs into a medium bowl and mix. Leave to one side.
Place the caster sugar, eggs and vanilla into a large bowl or the bowl of your stand mixer and mix until light and fluffy, about 1 minute on med-high speed.
Pour in the melted chocolate mix.
Mix until well combined and smooth.
Add in the dry ingredients and mix until well combined and smooth.
Place batter into your lined cake tin and level off with a spoon or spatula.
Place in the oven for 20-25 minutes until slightly puffy and an inserted skewer comes out with a few crumbs on it.
Leave to cool in the tin completely before slicing. Once cooled cut into 9-12 pieces.
Blondies will keep in an airtight container at room temperature for 4 days.