01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, beat together unsalted butter, brown sugar, and granulated sugar until light and fluffy.
03 - Add eggs one at a time, beating well after each addition. Stir in vanilla extract.
04 - In a separate bowl, whisk together all-purpose flour, baking soda, salt, and ground cinnamon.
05 - Gradually add dry ingredients to the creamed mixture, mixing until just combined. Fold in rolled oats and raisins.
06 - Drop tablespoon-sized portions onto prepared sheets, spacing them about 2 inches apart. Bake 11 to 13 minutes until edges turn golden and centres are set.
07 - Allow cookies to cool on baking sheets for 5 minutes before transferring to wire racks to cool completely.
08 - In a saucepan over medium heat, melt unsalted butter. Stir in brown sugar and cook, stirring, for 2 minutes.
09 - Add whole milk and bring mixture to a gentle boil. Remove from heat and let cool for 5 minutes.
10 - Whisk in sifted powdered sugar, vanilla extract, and a pinch of salt gradually until smooth and spreadable.
11 - Spread the caramel frosting evenly over cooled cookies. Allow frosting to set before serving.