Begin by soaking the raisins in a small bowl with the spiced rum. Stir the raisins occasionally to ensure that all raisins are submerged in the rum. The raisins should soak for a minimum of 30 minutes.
While the raisins are soaking, preheat your oven to 375°F and gather the remaining ingredients.
Cut the cold butter into cubes to allow it to mix more easily into the flour.
In a large bowl, sift the flour and add the baking soda, sugar, and salt. Whisk to combine. Use your fingers or a pastry blender to mix the butter into the flour mixture until it resembles coarse crumbs.
Drain the raisins and then stir them into the flour mixture. Using a wooden spoon or a spatula, stir in the buttermilk just until the dry ingredients are moistened and the dough comes together.
Pour the dough onto the counter and knead it gently about 8 times. The dough should be smooth, but still a little sticky. If it sticks too much while kneading, use a bench scraper. Avoid adding flour to the mixture, as it will dry out the dough.
Next, roll the dough into a 6-inch disc (approximately 1.5 inches tall). Place the dough on a baking sheet covered with parchment paper or a silpat. Use a sharp knife (or a razor blade) to make a ½ inch deep slash all the way across the bread. Repeat the slash to form a cross.
Bake the bread on the middle rack of the oven for approximately 30 minutes or until the bread is golden brown and a toothpick inserted into the bread comes out clean. The internal temperature should be about 190°F if you have an instant-read thermometer.
Place a clean linen or cotton towel on a wire rack and place the warm bread on top. Fold the towel over the bread loosely and allow the bread to cool until it is at room temperature. This should take approximately 40 minutes, depending on the temperature in your kitchen. Once it has cooled, it is ready to be eaten!