Brown butter is not essential in making this recipe, you could just as easily use simply melted butter. However, it does give the whole bake a wonderful flavour, so I think the extra effort is well worth it!
Once you combine the butter and sugar, keep mixing it all together. It takes a few minutes, but eventually the mixture will turn pale and creamy. Be patient, it's worth it!
Fold the dry ingredients in rather than beating in. This is to prevent overworking the gluten in the flour, so keeping the cookies tender and chewy, and not tough.
When pushing the reserved mini eggs into the top of the cookie, don't be afraid to give it a push to break the top crust of the cookie. As the eggs settle into the warm cookie dough, they will melt slightly and become one with the top crust.
Leave to cool completely before attempting to cut this up. The cookie dough is likely to still be soft once out of the oven, so cooling allows it to firm up and not fall apart when cut.
Use a really sharp knife to cut the bars. Try running the knife until hot water for a few seconds before cutting it. Not only will it make it easier to cut, but it will give you wonderful clean slices too.