Preheat oven to 180°C (350°F) (gas 4).
In a large mixing bowl, beat together the butter and sugars until creamy.
Then beat in the eggs and vanilla essence/extract until the mixture is smooth.
Sift the flour and bicarbonate of soda/baking soda and fold into the mixture. Then stir in the oats and raisins until the raisins are evenly distributed. The dough will be quite stiff.
Spoon rounded tablespoons of the dough onto the baking sheets, spaced well apart. The dough should make 4 dozen cookies. This may need to be done in two batches. Just make sure the baking trays/cookie sheets are allowed to cool before spooning the remaining batch of dough mixture onto them.
Bake for 10–12 minutes or until light golden brown.
Cool for 1 minute on the tray and then remove to a wire rack to cool completely. Store in an airtight container.