After the success of attempt one I baked these again today adapting based on the notes I made last time. I changed the butter/olive oil ratio - using 50g of butter and 34g of olive oil this time instead of an even split. I also reduced the sugar by 9 or 10g to 55g. Both of these were successful and they taste great.

They took almost twice as long to bake as they should have done - not sure if that’s because of the alterations or because of the temperature I used - 155 degrees (based on a fan oven). Maybe next time I’ll try at 165 degrees and see how that goes.