Step 1

Measure Sourdough Starter; let stand at room temperature for 30 minutes. Combine 2-1/2 cups of the flour and the yeast; set aside. Heat and stir water, sugar, butter, and salt just until warm (120 degree F to 130 degree F) and butter almost melts. Add water mixture to dry mixture. Add Sourdough Starter. Beat with an electric mixer on low to medium speed for 30 seconds, scraping bowl. Beat on high speed for 3 minutes.

Step 2

Combine 2-1/2 cups of the remaining flour and the baking soda. Add to yeast mixture. Stir until combined. Stir in as much remaining flour as you can.

Step 3

Turn dough onto a lightly floured surface. Knead in enough remaining flour to make a moderately stiff dough (6 to 8 minutes total). Shape dough into a ball. Place dough in a greased bowl; turn once. Cover and let rise in warm place until double in size (for 45 to 60 minutes).

Step 4

Punch dough down. Turn dough out onto a lightly floured surface. Divide dough in half. Cover and let rest for 10 minutes. Lightly grease baking sheet.

Step 5

Shape by gently pulling each portion into a ball, tucking edges beneath. Place on prepared baking sheet. Flatten each ball slightly to 6 inches in diameter. Using a sharp knife, make crisscross slashes across tops of loaves. Cover and let rise in a warm place until nearly double in size (about 30 minutes).

Step 6

Bake in a 375 degree F oven for 30 to 35 minutes or until bread sounds hollow when you tap the top. (If necessary, cover loosely with foil the last 10 minutes of baking to prevent overbrowning.) Immediately remove bread from baking sheet. Cool on wire racks. Makes 2 loaves (24 to 36 servings).