Preheat the oven Preheat your oven to 180°C (160°C fan) or Gas Mark 4. Line a baking tray with parchment paper.
Cream the butter and sugars In a large bowl, beat together the butter, light brown sugar, and granulated sugar until light and creamy.
Add the wet ingredients Beat in the egg and vanilla extract until fully combined.
Mix the dry ingredients In a separate bowl, sift together the flour, bicarbonate of soda, cinnamon, and salt.
Combine wet and dry ingredients Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Add oats and raisins Fold in the rolled oats and raisins until evenly distributed.
Shape the cookies Using a tablespoon or your hands, scoop out the dough and shape into small balls. Place them on the lined baking tray, leaving space for spreading.
Bake Bake in the preheated oven for 10–12 minutes or until the edges are golden brown (the centres may look slightly underdone).
Cool and serve Allow the cookies to cool on the baking tray for 5 minutes, then transfer them to a wire rack to cool completely.