National Trust Biscuits

My Mum used to make these - they were a regular request from my sisters and me - we loved them. I guess she got the recipe from the National Trust somehow or other: they were always National Trust biscuits, never any other or more descriptive name. I started making them myself as a teenager - they were easy enough for me to manage with limited skills, and always went down well... Despite my not knowing what a 'cup' measure was - I'd just pick a cup or mug from the cupboard and use that, so every time I made them they were different, depending on the cup I'd chosen. I still need to figure out my favourite interpretation of the 'cup' volume - sometimes they were slightly bendy and chewy when cooled; sometimes they'd spread out massively and all run into one another. The version I made yesterday (because I felt like it, because I wanted biscuits for journal club, because they seemed seasonal with all that warming ginger and treacle) came out fairly crispy and didn't spread that much - perhaps not my favourite - this recipe may be updated...

Mix in a bowl:
1 cup SR flour (1 cup plain flour plus 2 tsp baking powder)
1 cup sugar
1 cup oats
1 tsp ground ginger

Heat in a pan:
4 oz margarine (or coconut oil)*
1/2 tbsp black treacle (or molasses)

Mix in a mug:
1/2 tsp bicarbonate of soda
1/2 tbsp boiling water.

Heat oven to 300F / 150C. Grease a couple of baking sheets. Add the contents of the pan and the mug together to the bowl and mix until combined into a dough. Roll into balls, flatten slightly and space out on the baking sheets. Bake for 10-15 min, until golden brown and slightly spread. Let cool for 10 min or so on the baking sheet before transferring to a rack to finish cooling (they will be floppy when you first take them out; you want to transfer them at the sweet spot when they are slightly bendy and not completely hardened and crisp yet).

*tried using 3 oz sunflower oil, felt like would need a bit more?