Soften yeast in the warm water.
Blend in sugar and let stand 10 minutes.
Sir in sourdough starter and salt.
Add 1 1/2 cups of the flour and beat with an electric mixer for 3 to 4 minutes.
Mix 1 cup of the flour with soda and stir into batter.
Add remaining flour, if needed, to make a stiff dough.
Grease hands and shape dough into a loaf (dough will be slightly sticky).
Place in well-greased Bread 'n Cake Bake pan; cover.
Place in Crock-Pot.
Cover and bake on a High setting for 2 to 3 hours.
Remove pan and uncover.
Let stand for 5 minutes.
Unmold on cake rack; brush crust with butter and serve warm.