Food coloring - yellow, green, purple (or a combination of blue and red to make purple)
For the icing:
Pinch of salt
1Tablespoonunsalted butter, melted
4Tablespoonswhole milk or heavy cream
To make the dough:
In a mixing bowl, combine the warm water, yeast and 1 Tablespoon of the granulated sugar. Allow to sit for 5 minutes until it blooms. Meanwhile, in a small saucepan over medium heat, heat the butter, 4 Tablespoons of the sugar and the salt while constantly stirring. Once the butter is melted, stir in the sour cream and heat to luke warm.
Once the yeast is active, whisk in the warm butter and sour cream mixture, the egg and 1 cup of the flour. Whisk until smooth. Using an oiled wooden spoon, mix in small amounts of the remaining flour until a soft dough is formed (about another 2 cups of flour). The dough should be tacky, but not sticky.
Turn the dough out onto a lightly floured surface. With oiled hands, knead dough until elastic, about 5 to 10 minutes. Alternatively, use your stand mixer fitted with the dough hook to knead for 5 minutes. Add more flour by the teaspoon if needed. The dough should clear the sides of the bowl.
With floured or oiled hands, shape the dough into a ball and transfer to a well-oiled bowl, flipping once to cover with oil. Cover tightly with plastic wrap and allow to rise in a warm, draft-free area until it has doubled in size, about 1 1/2 to 2 hours.
For the filling:
Near the end of the dough rising, make the filling. Combine the melted butter, cinnamon and sugar in a medium bowl. Stir until fully incorporated.
Once the dough has doubled in size, turn it out onto a lightly floured surface and roll into a giant rectangle, about 18 inches by 14 inches wide.* Spread the cinnamon sugar mixture evenly over the dough, leaving a 1-inch border around the outside of the dough.
Roll the cake up jellyroll-style and pinch the seams tight. Carefully transfer the roll to a parchment- or silicone- lined baking sheet, seam-side down. Pull the ends together to form an oval or circle, then press to completely seal the shape.
Cover the cake with a clean kitchen towel and allow to rise for another 30 minutes. During this second rise, preheat the oven to 375 degrees F.
After 30 minutes, remove the kitchen towel and bake the cake in the center of the preheated oven for 25 minutes or until golden brown. Allow to cool completely on a wire rack before icing.
For the colored sugars:
While the cake is cooling, make the colored sugars. Place ½ cup of sugar into three separate small bowls. Drop green food coloring into one bowl and stir until evenly mixed and colored. Use the back of a small spatula or spoon to grind the sugar granules together and against the bowl for even coating, until there are no clumps. Repeat for the other two bowls of sugar to create one bowl of yellow sugar and one bowl of purple sugar (a mix of red and blue food coloring).
For the icing:
Once the cake is completely cooled, make the icing. Whisk together the powdered sugar, salt, vanilla, melted butter and milk until smooth. The icing should be at a consistency where it can easily drizzle onto the cake, but not run completely off of it. Whisk in more powdered sugar to thicken, or more milk to thin.
Transfer the cake to serving platter. (At this point, you can stick a dried bean or little plastic baby in through the bottom of the cake if you wish to carry on this Mardi Gras tradition. This is obviously completely optional.) Slide pieces of wax paper under the sides of the cake so that it can catch any overflow of icing or sprinkles of sugar, but make sure the wax paper can easily be removed.
Drizzle the icing evenly over the cake and allow to ooze down the sides and middle. Immediately (before the icing has a chance to set) sprinkle on rotating strips of the colored sugars. Work this step speedily, as the icing sets very quickly. Slide the wax paper pieces out from under the cake and discard. Serve within 1 or 2 days, warm or at room temperature.
*Recipe Note: Careful not to roll it out too thin. I think my dough should've only been about 16 inches by 12 inches as it decided to burst (or stick it's tongue out at me during baking). But, I remedied it by cutting off it's "tongue". :)