Preheat your oven to 375oF (190oC)
Cut a big piece of baking paper and set aside.
Use a medium bowl to combine the dry ingredients, apart from the sugars. Set aside.
Use a large bowl to cream the butter, white and brown sugar together; add the egg and the vanilla and whip until combined
Add the dry ingredients into the wet ingredients and mix with a spatula until the flour has just absorbed, do not over mix.
Fold in the oats and the raisins.
Use a tablespoon measure scoop heaped tablespoons of the cookie dough onto your lined baking paper, leaving about 1 1/2 to 2 inches between the cookies.
Bake for about 9-10 minutes or until the cookies are golden brown and slightly risen. Don't be tempted to bake for longer or you will loose the gooey center.
Allow the cookies to cool slightly before transferring on to a wire rack to cool fully.
Store in an airtight container for up to 3 days at room temperature.