Preheat oven to 350°F and place rack in center of oven. Grease an 8” x 8” pan and line with parchment or wax paper, leaving an overhang on two opposite sides to assist with removal later.

Melt the butter in a sauce pot over medium heat. Add flour and stir until you create a light brown paste (roux). Add the sweetened condensed milk slowly, stirring constantly, and incorporate thoroughly into the roux. Add the salt and rum, and continue heating until the mixture is nice and thick. Set aside and allow to cool slightly.

Combine the oats and 1 cup of graham cracker crumbs in a large mixing bowl. Add the milk mixture to the oats and graham crackers and stir until thoroughly coated. Spread the mixture in the prepared pan and pat firmly to distribute evenly.

Top the mixture with the chopped chocolate, followed by the marshmallows. Sprinkle the remaining 1/2 cup of graham cracker crumbs on top. Use the flat of your hand to gently press on the top layers.

Bake for 15 minutes, turning the pan halfway through to promote even baking.

Optional: after baking, brown the marshmallows by placing under the broiler for a minute or two. Do not walk away from the oven — the marshmallows will brown very quickly!

Remove and allow to rest in the pan for 15 minutes. Use the parchment paper overhang as handles to easily remove the bars from the pan and place on a cooling rack. Use a sharp knife to cut the bars — they’ll be ooey, gooey and wonderful.