1. Put the butter and sugars to a large bowl and beat together until pale, fluffy and creamy. We use an electric mixer, but you can use a wooden spoon too.
2. Add the egg and vanilla and mix well.
3. Tip in the plain flour, oats, baking powder, bicarbonate of soda and salt, then beat until it all comes together into a soft cookie dough.
4. Stir through the raisins until they’re evenly dotted through the dough.
5. Gently roll into balls and put them on trays. Chill the dough in the freezer for at least 30 minutes, or in the fridge for about an hour.
6. While the dough is chilling, preheat your oven to 200ºC / 180ºC fan (lower if your oven tends to be on the hot side).
7. Place the chilled cookie dough balls onto a lined baking tray, allowing room for them to spread.
8. Bake for 12 - 14 minutes, until golden around the edges but still soft in the middle.
9. Leave the cookies to cool on the tray for at least 30 minutes – they’ll continue to cook and firm up as they cool.