Pre-heat the oven to 350°F.

Combine the butter, brown sugar and white sugar in a bowl and use an electric hand mixer to cream the ingredients together until they are light and fluffy. Add the egg and vanilla extract and combine. In a separate bowl, combine the flour, oats, cinnamon, baking soda and salt. Add the dry ingredients to the wet ingredients and stir until just combined. Fold in the raisins.

Drop heaping tablespoons of the cookie dough onto a baking sheet, spacing them 2-inches apart. Transfer the baking sheet to the center rack of the oven and bake at 350°F for 8 to 10 minutes.

Let the cookies cool for a minute or two and then transfer them to a cooling rack.

When the cookies have cooled completely, make the icing glaze by combining the powdered sugar and milk in a bowl and whisking until smooth. Drizzle the icing glaze over cookies. Let the icing set up before serving or storing the cookies. If you’re not serving the cookies right away, store them in an airtight container.