In a large mixing bowl, COMBINE warm water, yeast and sugar; STIR to dissolve: let STAND until foamy, about 5 minutes.

Meanwhile, in a 1-quart saucepan, COMBINE buttermilk, butter, and sugar; HEAT over medium-low until warm.

ADD warm buttermilk mixture to yeast mixture, along with salt; ADD flour, holding the 1/4 cup for later; BEAT with a wooden spoon until blended.

TURN dough onto lightly floured surface; KNEAD until smooth and elastic, about 10 minutes, working in just enough of the remaining 1/4 cup flour to keep dough from sticking.

SHAPE dough into a ball; PLACE in large greased bowl, turning dough to coat; COVER with plastic wrap; let RISE in a warm place until doubled in volume, about 1 hour.

PUNCH down dough; TURN dough onto lightly floured surface; CUT in half; COVER; let REST 15 minutes.

Lightly GREASE two 8½" x 4½" metal loaf pans.

SHAPE each dough half into a 9" x 6" rectangle; ROLL up from short side; PINCH seam and ends to seal.

PLACE a loaf, seam side down, in each pan; COVER; let RISE in warm place until doubled in volume, about 1 hour.

PREHEAT oven to 375°; MELT remaining butter.

Using a serrated knife, CUT a lengthwise slash, about ¼" deep, in each loaf; BRUSH loaves with melted butter.

BAKE until golden and loaves sound hollow when lightly tapped on bottom, about 25 to 30 minutes.

REMOVE from oven; COOL on wire racks.