Line the tin with parchment paper. Preheat the oven to 180C/350F while you make the blondies.
In a large mixing bowl, combine the butter, brown sugar and white chocolate. Melt together in the microwave in 10-20 second bursts, stirring in between, until completely melted. Once done, keep mixing the ingredients until they come together into a smooth fudgy mixture. This step can take a few minutes and plenty of patience, but be patient, I promise it will come together!
Add the eggs and vanilla into the bowl one at a time. Mix well to combine in between additions. The mixture will be thick and glossy.
Sift in the flour and salt, then fold in gently to combine. Add in the white chocolate chips and about half the mini eggs, roughly crushed (save the rest, unbroken, to top the blondie). Fold together to mix in thoroughly.
Tip the blondie mixture into the prepared tin and spread out to level.
Bake in the preheated oven for 15 minutes. At 15 minutes, remove the tin from the oven and evenly scatter the reserved mini eggs over the top. Press gently to ensure they bake within the top. Return the tin to the oven and bake for the remaining 10-15 minutes. Look for the blondies to have very little to no jiggle in the middle and for the edges to be shrinking away from the sides slightly.
Remove from the oven and leave to cool in the tin for 5 minutes before transferring to a cooling rack to cool completely. Once cool, cut into squares and enjoy!