line a 20cm x 20cm silicone mould with overhanging parchment paper on all sides - no need for non-stick spray.
in a large mixing bowl, combine entire contents of brownie mix with eggs and melted + cooled butter, using a balloon whisk.
pour the mix into your baking mould and bake for 35 mins.
meanwhile, de-shell and roast hazelnuts for 5 minutes under a medium-hot grill (broiler) or 10 minutes in the oven at 200C fan (220C static), then remove as much skin as possible by rubbing between your fingers or in a lint-free tea towel, and finally, crush them so as to obtain crumbs.
let the brownie cake cool in its baking mould, then spread Keto Nut.ella all over the top and refrigerate.
when the nut.ella has firmed up a bit, remove from fridge and sprinkle hazelnut crumbs all over the top, then press down lightly with your palm.
lift the cake out of the mould, discard baking paper and cut into 16 squares.
Notes
Keep refrigerated and preferably in a sealed container.
Metric kitchen scales are an inexpensive yet invaluable gadget to enable accurate measurement of ingredients. Store them upright in a cupboard or over your worktop and they'll only take up a tiny bit of space. Click HERE for the ones I use.