Preheat the oven to 400 degrees.
Place the flour, baking soda, and salt in a large food processor (9 cup or larger capacity) with the dough blade. Mix briefly, and then add the cold butter and process until the mixture has a crumb-like texture. If you don't have a food processor that's big enough, you can place the dry ingredients in a large bowl and cut in the butter by hand with two forks or a pastry blade.
In a large bowl, combine the buttermilk, egg, and maple syrup. Add this to the food processor and process until a ball of dough forms.
Place the dough in the large bowl and add the raisins. Mix the raisins into the dough with your hands. The dough should be sticky.
Form the dough into a ball and press down slightly. Place it in a large, buttered cast iron skillet. Use a sharp knife to score the dough, placing an "x" across the top (about 1/2 inch deep).
Bake the loaf for 40 to 45 minutes, until nicely browned and a toothpick inserted in the center comes out clean.
Brush with melted butter while cooling. If you can get your hands on Kerrygold butter (or other butter from grass-fed cows), this is the perfect spread for a warm piece of Irish soda bread.