Cook first 4 ingredients in a medium saucepan over low heat, stirring often, until butter melts. Set aside, and cool mixture to 100° to 110°.
Stir together yeast, 1/2 cup warm water, and 1 tablespoon sugar in a 1-cup glass measuring cup; let stand 5 minutes.
Beat sour cream mixture, yeast mixture, eggs, and 2 cups flour at medium speed with a heavy-duty electric stand mixer until smooth. Reduce speed to low, and gradually add enough remaining flour (4 to 4 1/2 cups) until a soft dough forms.
Turn dough out onto a lightly floured surface; knead until smooth and elastic (about 10 minutes). Place in a well-greased bowl, turning to grease top.
Cover and let rise in a warm place (85°), free from drafts, 1 hour or until dough is doubled in bulk.
Punch down dough, and divide in half. Roll each portion into a 22- x 12-inch rectangle. Spread 1/3 cup softened butter evenly on each rectangle, leaving a 1-inch border. Stir together 1/2 cup sugar and cinnamon, and sprinkle evenly over butter on each rectangle.
Roll up each dough rectangle, jelly-roll fashion, starting at 1 long side. Place one dough roll, seam side down, on a lightly greased baking sheet. Bring ends of roll together to form an oval ring, moistening and pinching edges together to seal. Repeat with second dough roll.
Cover and let rise in a warm place (85°), free from drafts, 20 to 30 minutes or until doubled in bulk.
Bake at 375° for 14 to 16 minutes or until golden. Slightly cool cakes on pans on wire racks (about 10 minutes). Drizzle Creamy Glaze evenly over warm cakes; sprinkle with colored sugars, alternating colors and forming bands. Let cool completely.
Cream Cheese-Filled King Cake: Prepare each 22- x 12-inch dough rectangle as directed. Omit 1/3 cup softened butter and 1 1/2 teaspoons ground cinnamon. Increase 1/2 cup sugar to 3/4 cup sugar. Beat 3/4 cup sugar; 2 (8-ounce) packages cream cheese, softened; 1 large egg; and 2 teaspoons vanilla extract at medium speed with an electric mixer until smooth. Spread cream cheese mixture evenly on each dough rectangle, leaving 1-inch borders. Proceed with recipe as directed.
*6 to 6 1/2 cups all-purpose flour may be substituted.
This recipe uses bread flour, which makes for a light, airy cake. You still get tasty results with all-purpose flour--the cake will just be more dense.