A note before I share the recipe, these cookies are slim and crisp - they stay deliciously chewy in the centre but they're definitely not chunky, melty cookies; the book says "these are easy to make and absolutely delicious. They develop a butterscotch flavour as they bake and are extremely fragile." So there you go!
To make about 20 cookies
225g unsalted butter, softened
225g soft brown sugar
1/2 tsp salt
1/2 tsp vanilla essence
1 large egg
190g plain flour, sifted
220g dark chocolate chips*
**The Valentine's twist here is that I added pink and white mini marshmallows - not particularly radical, but delicious all the same. I also made half a batch with white chocolate chips for my mum.
Preheat the oven to 180C and line a baking tray with parchment paper.
Combine the butter, brown sugar, salt, vanilla and egg in a large bowl. Use an electric mixer or beat by hand to a smooth batter. Add the flour and chocolate chips/marshmallows and mix until no traces of flour remain.
Drop the batter by heaping tablespoonfuls on the baking sheet, spacing the cookies 2 inches apart. Bake until the edges of the cookies are barely brown, 6 to 8 minutes. Remove and let cool on a wire rack.
Adjustment: I found that the cookies turned out better when I spaced them further apart - you might only be able to bake 5 or 6 at a time - and didn't spread out as much in the oven when I refrigerated the batter in between batches. When they came out of the oven, I placed the tray by a window to let them cool slightly before manoeuvring them onto the wire rack - they were too soft to move without doing that.