In a small bowl, combine the warm water, yeast, and 1 teaspoon of sugar. Stir gently and let sit for 5 to 10 minutes until the mixture becomes foamy.
In a large mixing bowl, whisk together 3 cups of flour, the remaining 1 tablespoon sugar, and salt.
Add the warmed buttermilk, melted butter, and the activated yeast mixture to the dry ingredients. Stir with a wooden spoon or dough hook until combined.
Gradually add the remaining 1/2 cup flour, a little at a time, kneading the dough until it is soft, smooth, and slightly sticky but pulls away from the sides of the bowl.
Turn the dough onto a lightly floured surface and knead for about 8 to 10 minutes until elastic and smooth. Add small amounts of flour as needed to prevent sticking but avoid adding too much.
Place the dough in a lightly greased bowl, turning once to coat the surface. Cover the bowl with a clean kitchen towel or plastic wrap and let the dough rise in a warm, draft-free place for about 1 hour or until doubled in size.
Punch down the dough to release air. Turn it out onto a lightly floured surface and shape it into a loaf.
Place the shaped dough into a greased 9×5-inch loaf pan. Cover loosely with a towel and let rise again for 30 to 40 minutes until the dough has risen about 1 inch above the rim of the pan.
Preheat the oven to 375°F (190°C).
Bake the bread in the preheated oven for 30 to 35 minutes until the top is golden brown and the loaf sounds hollow when tapped.
Remove the bread from the oven and let it cool in the pan for 10 minutes. Then transfer the loaf to a wire rack to cool completely before slicing.