Stir together first 3 ingredients in a 1-cup glass measuring cup; let stand 5 minutes.
Stir together 4 1/2 cups bread flour, salt, and baking soda.
Beat yeast mixture and 1/2 cup bread flour at medium speed with a heavy-duty electric stand mixer until well blended. Gradually add sweet potato, next 5 ingredients, and flour mixture, beating until well blended.
Turn dough out onto a well-floured surface, and knead until smooth and elastic (about 4 to 5 minutes), gradually adding remaining 1/2 cup bread flour.
Place dough in a lightly greased large bowl, turning to grease top. Cover and let rise in a warm place (85), free from drafts, 1 to 1 1/2 hours or until doubled in bulk.
Stir together 2/3 cup granulated sugar and next 2 ingredients. Punch dough down; turn out onto a well-floured surface. Divide dough in half.
Roll 1 portion into a 16- x 12-inch rectangle.
Brush with half of 1/4 cup melted butter.
Sprinkle with half of sugar mixture.
Cut dough lengthwise into 6 (2-inch-wide) strips using a pizza cutter or knife.
Loosely coil 1 strip, and place in center of a lightly greased 10-inch round pan. Loosely coil remaining dough strips, 1 at a time, around center strip, attaching each to the end of the previous strip to make a single large spiral. (Sugared sides of dough strips should face center of spiral.) Repeat with remaining dough half, butter, and sugar mixture.
Cover and let rise in a warm place (85), free from drafts, 30 minutes or until doubled in bulk.
Preheat oven to 35
Bake 30 minutes or until lightly browned and done. Cool in pans on a wire rack 10 minutes.
Remove from pans to serving plates. Prepare Caramel Glaze, and brush over swirls.
