Heat the buttermilk, butter and sugar in a pot until simmering; whisk in the baking soda, then let cool to lukewarm. Meanwhile, put 1/4 cup lukewarm water in a bowl and stir in the yeast; let stand 5 minutes. Whisk the yeast mixture into the buttermilk mixture.
Whisk the flour and salt together in a large bowl. Add the liquid and mix until a soft dough forms. Knead the dough in the bowl until it comes together and is smooth, about 2 minutes. Cover with plastic wrap and let stand 30 minutes.
Butter a 9-by-13-inch glass baking dish. Divide the dough into 12 pieces and roll each piece into a ball. Arrange the balls in the buttered dish. Lightly cover with plastic wrap and let rise until nearly doubled in size, about 1 1/2 hours.
Preheat the oven to 425 degrees F.
Bake the rolls until puffed and golden brown, about 15 minutes. Serve warm.