Heat the oven to 190C/170C fan. Butter a deep 20 x 20cm brownie tin, and line the base and sides with baking parchment. Melt the butter and white chocolate in a heatproof bowl set over a pan of simmering water, stirring now and then until smooth. Remove from the heat and leave to cool for 5 mins.

Tip the muscovado and caster sugars and the eggs into a large, clean bowl and whisk for 2 mins until the mixture is thick and foamy. Whisk a quarter of the mixture into the melted chocolate and butter mixture along with the vanilla. Carefully fold in the rest of the egg mixture until smooth, then fold in the flour, baking powder and a pinch of salt until everything is combined. Roughly chop 100g of the mini chocolate eggs, then fold into the batter. Pour the batter into the tin and gently shake to level the surface. Press half of the remaining whole mini chocolate eggs into the top.

Bake the blondies for 45-50 mins. Check they are cooked by giving the tin a gentle shake – they should be mostly set, with a slight wobble in the centre. Remove from the oven and immediately press the rest of the whole mini chocolate eggs into the top (these can be roughly crushed or halved first for a different texture, if you like). Leave to cool completely in the tin. Don't worry if the mixture sinks slightly. Once cooled, the blondies will be gooey, fudgy and moist, cut into squares and serve. Will keep in an airtight tin for up to four days.