Irish Brown Soda Bread

1 1/2 cups all-purpose flour, plus more for dusting 

1 1/2 cups whole-wheat flour

2 tsps. sugar

1 1/2 tsps. kosher salt

1 tsp. baking soda

2 tbs cold unsalted butter, cut into small cubes

1 1/2 cups cold buttermilk, plus more for brushing

Rolled oats, for topping

Preheat the oven to 400˚ F. Sift the all-purpose flour, whole-wheat flour, sugar, salt and baking soda into a large bowl. Add the butter and rub it into the flour mixture with your fingers until there are no visible pieces. Make a well in the center and add the buttermilk. Stir the buttermilk into the flour mixture with a large spoon until just combined (it will be shaggy and a little sticky). Scrape out the dough onto a floured surface. Lightly flour the top of the dough, then use floured hands to gently pat and smooth the top and sides of the dough into a flat 6-inch round, about 1 1/2 inches tall. Be careful not to overwork the dough. Sprinkle an 8-inch cast-iron skillet or round cake pan with flour. Transfer the dough round to the skillet or pan. Using a knife, score a 1/2-inch-deep cross on top of the dough, edge to edge. Brush the top with buttermilk and sprinkle with oats and sunflower seeds. Bake until the bread is puffed and golden brown and a toothpick inserted into the center comes out clean, 35 to 40 minutes. Loosen the sides with a paring knife; immediately remove the bread to a rack and let cool to room temperature, about 1 hour. Slice and serve.