3 1/2 cups all-purpose flour, plus more for work surface
1/4 cup sugar
1 teaspoon baking powder
1 teaspoon baking soda
3/4 teaspoon salt
1/2 cup (1 stick) unsalted butter, cut into small cubes and frozen, plus more, softened, for skillet
1 (8-ounce) container sour cream
1 large egg
2 cups raisins
1 cup buttermilk
Caraway seeds (optional)
Preheat oven to 375 degrees with a rack set in lower third of oven. Lightly butter a 10-inch round cast-iron skillet; set aside.
In a large bowl, whisk together flour, sugar, baking powder, baking soda, and salt. Add butter, sour cream and egg; mix, using a pastry blender, until mixture resembles coarse crumbs. Stir in raisins, buttermilk, and caraway seeds, if using, and mix until a sticky dough forms.
Turn dough out onto a lightly floured work surface. Using a floured bench scraper, form into a round loaf; using a sharp knife score a large “X” in the center.
Place in prepared skillet and transfer to oven. Bake until loaf is golden brown and a toothpick inserted into the center comes out clean, about 1 hour. If top begins to brown too quickly, loosely cover with a piece of parchment paper-lined aluminum foil. Transfer to a wire rack to cool.