1. Stir together first 3 ingredients in a 1-cup glass measuring cup; let stand 5 minutes.
2. Stir together 4 1/2 cups bread flour, salt, and baking soda.
3. 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.
4. 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 (85º), free from drafts, 1 to 1 1/2 hours or until doubled in bulk.
5. 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.
6. 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.
7. Cover and let rise in a warm place (85º), free from drafts, 30 minutes or until doubled in bulk.
8. Preheat oven to 350º. 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.