Place the raisins into a plastic container and cover them with the rum. Cover the container and set it aside for at least 48 hours, but up to a week is better. Shake the container half way through the soaking time. The raisins should absorb almost all of the rum.
Preheat the oven to 350 and prepare a baking sheet with parchment or a silicone mat.
Mix the flour, baking powder, baking soda and salt together and set aside.
Beat the butter and sugar with a paddle attachment until it’s light and fluffy. Add in the egg and vanilla. Gradually add in the flour mixture on low speed until it’s just combined. Remove from the mixer and hand stir in the chocolate chips and raisins. Add up to 1 tablespoon of the excess rum, discard the rest.
Measure out a tablespoon of batter and place them on the prepared cookie sheet. Bake for 15 minutes. The edges should be browned but the center will still be pale. Remove from the oven and sprinkle sea salt over them. Let the cookies rest on the cookie sheet for 5 minutes before transferring to a cooling rack.
Enjoy your adult Rum Raisin Oatmeal Chocolate Chip Cookies with a big glass of milk.