In the bowl of a stand mixer fitted with the dough hook attachment, combine flour, ⅓ cup sugar, yeast, and zest. With mixer on low speed, add warm milk, eggs, and vanilla, beating until mixture comes together, 2 to 3 minutes.
With mixer on medium speed, add ½ cup butter, 1 tablespoon at a time, letting each piece incorporate before adding the next. Add salt, beating just until combined, about 3 minutes. Increase mixer speed to medium, and beat until a smooth and elastic dough forms and pulls away from sides of bowl.
Spray a large bowl with cooking spray. Place dough in bowl, turning to grease top. Cover and let rise in a warm, draft-free place (75°) until doubled in size, 1½ to 2 hours. After dough has risen, refrigerate for 30 minutes.
In the bowl of a stand mixer fitted with the paddle attachment, beat cinnamon, remaining ½ cup butter, and remaining ½ cup sugar at medium speed until creamy, 3 to 4 minutes, stopping to scrape sides of bowl. Fold in pecans.
Spray a 9x5-inch loaf pan with cooking spray.
On a heavily floured surface, roll dough into a 16x12-inch rectangle. (Dough will be sticky.) Spread pecan mixture onto dough, leaving a 1-inch border on long sides. Starting at one short side, roll up dough, jelly roll style, and press edge to seal. Using a sharp knife, cut roll in half lengthwise. Carefully twist dough pieces around each other, and place in prepared pan, cut side up. Cover and let rise in a warm, draft-free place (75°) until doubled in size, 1 to 1½ hours.
Preheat oven to 350°.
Bake for 30 minutes. Cover with foil, and bake until an instant-read thermometer inserted in center registers 190°, about 35 minutes more. Let cool in pan for 30 minutes; remove from pan.
In a small bowl, combine confectioners’ sugar and cold milk. Drizzle glaze over loaf, and top with Carnival Sugars.
Recipe by Louisiana Cookin' at https://louisianacookin.com/king-cake-babka/