Prep the Dough Liquids: Preheat the oven to its lowest setting (170°F/76°C) for 10 minutes, then turn it OFF. In a small saucepan, melt ½ cup butter, ½ cup brown sugar, and ½ cup milk on low heat. Do not boil! Cool for 5 minutes.
Knead and First Proof: In a stand mixer (paddle attachment), mix the all-purpose flour, yeast, salt, eggs, and vanilla on low for 2 minutes. Switch to the dough hook, slowly pour in the cooled butter mixture, and add the sour cream. Knead on low for exactly 10 minutes. Shape into a ball, place in an oiled bowl, cover with a towel, and place in the warmed, turned-off oven for 1.5 hours.
Colour the Dough: Punch down the dough and weigh it on a food scale. Divide the total weight by 6 to create 6 equal dough balls. Using a knife tip, place a tiny smear of gel colour into the center of one dough ball, fold to seal, and mix in the stand mixer (paddle attachment) until vibrant. Repeat for all 6 colours (Purple, Blue, Green, Yellow, Orange, Red). Keep dough covered with a towel.
Roll and Stack: Mix all of the cinnamon filling ingredients in a bowl. Cut parchment paper to fit a 12-inch round pizza pan. Roll the purple dough into an 11-inch disc and place it on the parchment. Lightly press a 10-inch bowl into the dough to mark a circle. Spread 2-3 Tablespoons of filling inside the circle. Roll the blue dough, stack it on top, and add filling. Repeat in rainbow order, ending with red (no filling on top of the red layer). Use a serrated knife to trim around the 10-inch bowl, to create a perfect circle of your stacked dough.
Cut and Twist (Flower Shape): Lightly mark a 2-inch circle in the exact center of the dough. Cut 16 equal slices (from the edge of the 2-inch center out to the perimeter). Take two adjacent slices and twist them away from each other twice. Pinch the ends together to form a heart-shaped petal. Repeat to create 8 petals. Slide the parchment onto your pizza pan or baking tray.
Second Proof and Bake: Cover the bread with a clean hand towel and return it to the warmed, turned-off oven to rise for 1 hour. Remove the bread and preheat the oven to 325°F (163°C). Brush the entire bread generously with the ½ cup melted butter. Bake on the middle rack for 20 minutes, then move to the bottom rack for 20 minutes. Cool for 15 minutes.
Glaze: Whisk the cream cheese, powdered sugar, milk, vanilla, and salt until smooth. Pipe over the warm bread and enjoy!