01 -
Leave the pan to chill on a rack for at least a couple of hours—overnight works great too. Then slice into squares.
02 -
Pop everything in the oven for 27 to 30 minutes till the sides look set and start to turn golden. The middle might look a little wobbly—don’t worry.
03 -
Scatter small pieces from the dough you saved, about 2.5 cm each, on top of the condensed milk. Don't stress about perfect coverage, just gently push them down.
04 -
Carefully pour about 227 grams of that condensed milk all over the top so it covers evenly.
05 -
Sprinkle the white chocolate chips on top of the pressed dough layer so they're spread out nicely.
06 -
Move a little more than half of your dough (up to two-thirds is fine) into the lined pan. Use a spatula or greased hands to flatten it out evenly.
07 -
Dump in the cake mix and the egg with your butter. Use low speed and mix it up until everything clumps into a dough.
08 -
Grab a big bowl and blend the soft butter using a handheld mixer set to medium-high until it's super creamy.
09 -
Turn the oven on to 175°C. Line your square pan with foil and spray it to keep things from sticking. Put it to the side for now.