Shape the Dough: Use a 2-tablespoon cookie scoop or spoon to scoop a small amount of the dough. Then shape them into balls and dunk them in the slivered almonds, coating them evenly. Press down so the almonds stick to the dough.
Place on Cookie Sheet: Place the cookies on the prepared baking sheet.
Brush with the Rum-Butter Mixture: Lightly brush each cookie with the rum butter. If the mixture has hardened, gently warm it in the microwave for a few seconds.
Bake: Then, bake at 350°F (175°C) for about 20 minutes. Check the bottom with a spatula: Bake until the bottom is nicely golden.
Brush with the Rum-Butter Mixture Again: Take the baking sheet out of the oven and quickly brush each cookie again with the rum butter.
Top with Flaky Sea Salt (Optional): Top with flaky sea salt, if using.
Cool: Let the cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.