Place butter and sugar in a stand mixer fitted with a paddle attachment. Beat on medium speed until creamy. Beat in syrup, eggs, and vanilla until combined.

In a medium separate bowl, combine flour, oats, cinnamon, baking soda, and salt. Add to liquid mixture and beat on medium speed until a dough forms. Mix in raisins and walnuts if using. (dough will be quite sticky)

Wrap dough in plastic wrap and refrigerate 45 minutes to 1 hour or until slightly firm.

Roll cookie dough into 1-in balls and place on parchment paper-lined baking sheets. Flatten dough balls slightly. Bake cookies at 350F 9-10 minutes or until edges just start to turn golden (cookies will appear underbaked---this is ok) Cool cookies on baking sheet 10 minutes before transferring to a wire cooling rack to cool completely.