Put the lukewarm buttermilk with sugar and yeast in a bowl and stir, let stand for 15 minutes.
Then add flour, salt and butter, knead until the dough starts to bubble. Cover and let rise in a warm place for about 40 minutes so that the volume doubles.
Then knead vigorously, put in a greased loaf pan (32 cm), let rise for another 20 minutes.
Bake in the preheated oven (180 ° C) on the lower rack for 35-45 minutes until golden brown.
TIP: Place a container with water on the wire rack while baking.