Step 1

Preheat oven to 350°F. Combine milk and vinegar in a bowl; let stand until curdled and thickened, about 5 minutes. Meanwhile, in a large bowl, whisk together both flours, wheat bran, sugar, salt, and baking soda; stir in caraway seeds and currants.

Step 2

Make a well in the center of the flour mixture. Add milk mixture and stir together, starting in center and working outward, until a sticky dough forms (do not overmix). Transfer to a generously floured work surface and, with floured hands, form a cohesive ball. (Do not overwork dough.)

Step 3

Pat ball into a 7-inch-wide domed round and transfer to a baking sheet. Cut a 1-inch-deep "X" with a floured knife across top of round. Using a wooden skewer, poke holes at 1-inch intervals to bottom of dough (about 28 holes total).

Step 4

Bake soda bread until cooked through and loaf sounds hollow when tapped on bottom, 1 hour and 10 minutes. Transfer to a wire rack and let cool completely before slicing and serving with butter. Bread can be made 2 days ahead and stored, whole, at room temperature, in a paper bag or wrapped in parchment.