Preheat oven to 350F. Combine rum and raisins in a small bowl and set aside. In a microwave-safe bowl, melt the butter. Add the sugars to the melted butter and whip by hand with a spoon until mixed. Allow mixture to cool a bit before adding the egg (just cool enough so you don’t end up with scrambled eggs) and stir. Then add all remaining ingredients & stir. Finally, fold in the soaking raisins and rum, including any rum that did not absorb into the raisins and was at the bottom of the bowl.
Examine your batter and based on how well your raisins did or did not soak up the rum, you may need to add more flour/more oats if the batter is looking too wet. My raisins did a poor job of soaking up the rum so I added another 1/4 c flour and another 1/4 c oats to get the batter into cookie dough consistency. Use common sense and judgment.
Also, chilling the dough in the freezer for 10 minutes before baking will help with wet dough and chilled dough will result in cookies that spread less while baking.
Scoop golf ball sized balls onto a cookie sheet, about 2 inches apart. They do spread. Bake at 350F for 10-12 minutes. Remove from oven even if they don’t look quite done; they will solidify more as they cool. Allow to cool well before removing the cookies from the cookie sheets.