Preheat the oven to 425°F. Brush a metal loaf pan liberally with some of the melted butter (a tablespoon or so, but you don’t need to be precise), and set the rest aside.
In a mixing bowl, thoroughly whisk together the flours, sugar, soda, and salt. In a small bowl, whisk together the yogurt, molasses, and remaining melted butter until smooth. Pour the beer over the dry ingredients, followed by the yogurt mixture, then use a spoon or spatula to gently combine the dough just until all the flour is moistened. Avoid overmixing.
Scrape the mixture into the loaf pan and gently spread it to fill the pan evenly. Bake for 15 minutes, then reduce the temperature to 350°F and bake for an additional 30 to 40 minutes more. Halfway through, brush the loaf with an additional tablespoon of melted butter if you’d like. Test for doneness using a toothpick or cake tester — but assess how the batter feels in the center rather than how the toothpick looks; when you insert the toothpick, it should feel as firmly set in the center as it does at the edges of the pan.
Leave in the pan for 5 minutes before tipping onto a rack, and cool completely before slicing. Leftovers toast beautifully.
