Preheat oven to 425° F. Put a dry, well-seasoned 9- to 9 1/2-inch cast-iron skillet in middle of oven to heat.
Stir together cornmeal, baking soda, and salt, crushing any small bits of baking soda. Whisk eggs in another bowl until blended and whisk in buttermilk.
Remove hot skillet from oven carefully and add butter, swirling gently to coat bottom and sides of skillet. (If butter begins to sizzle and brown around edges, so much the better.)
Whisk hot butter into buttermilk mixture and return skillet to oven. Stir cornmeal into buttermilk mixture just until moistened. (The batter does not have to be smooth, a few small lumps are good.)
Scrape batter into hot skillet and bake until golden, 20 to 25 minutes. Invert skillet over a platter and cool bread at least 3 minutes.
Serve with Buckwheat-Honey Butter.