1. Heat the oven to 350 degrees and coat a 9-by 13-inch baking dish with butter. In a medium bowl, whisk together the first six ingredients.
2. With a hand mixer or a stand mixer with paddle attachment, beat the butter until smooth. Add the dry ingredients, and blend at medium speed until the mixture resembles coarse crumbs, about 1 minute. Reduce the mixer's speed to low and add the eggs, one at a time, until just blended. Slowly add the buttermilk and blend evenly.
3. Pour the batter into the pan, and bake until the top is golden brown and a toothpick inserted in the middle comes out clean, about 20 minutes. Let bread cool for 15 minutes before slicing.