Preheat oven to 350 degrees F. In a large bowl beat butter with a mixer on medium 30 seconds. Add brown sugar, baking soda, and salt. Beat on medium 2 minutes, scraping bowl as needed. Beat in 1/3 cup maple syrup, egg, and 1 tsp. of the vanilla. Beat in flour on low. Stir in oats and raisins.

Drop dough by teaspoons 2 inches apart onto an ungreased cookie sheet. Bake 12 minutes or until edges are set and centers are still soft. Cool 2 minutes on cookie sheet. Remove; cool on wire rack.

In a small bowl stir together powdered sugar, the 3 Tbsp. maple syrup, and the remaining 1/2 tsp. vanilla. If necessary, add a milk or water, 1/2 tsp. at a time, to desired consistency. Drizzle over cooled cookies.