Scald the buttermilk. It will begin to curdle. Add butter, sugar and salt. Stir. Let it rest till lukewarm. Add yeast to warm water, stir. Add it to lukewarm buttermilk mix.
Whisk together flour and soda.
Add flour to wet ingredients. Stir till thoroughly mixed and you get a shaggy dough. Transfer the dough to a floured counter and knead for about 5 to 6 minutes. The dough should become really soft and supple.
Transfer the dough to an oiled bowl. Turn the dough so that it is coated with oil on all sides. Cover with a kitchen towel and keep in a warm place until it doubles in size.
Punch the dough and knead for another 2 to 4 minutes. Shape into a loaf. Place it into 8 ½ inch x 4 ½ inch greased loaf tin. Cover and keep it to rise for another one hour or until doubled.
Bake in a preheated oven at 190 degrees C for 30 -35 minutes till the top turns brown and the pan sounds hollow when tapped at the bottom. Tent with a foil if the bread browns too early.
Remove from the oven. Remove from the pan after 10 minutes. Cool in the rack. Slice next day.