01 - Combine warm milk and melted butter in a small bowl. Sprinkle yeast over the surface and let stand for 5 minutes until foamy and activated.
02 - In a large bowl or stand mixer, combine the yeast mixture with granulated sugar, eggs, vanilla extract, and salt. Gradually incorporate flour until a soft, slightly sticky dough forms.
03 - Knead on a lightly floured surface for 6–8 minutes by hand or 5 minutes with a dough hook until smooth, elastic, and no longer sticky.
04 - Place dough in a greased bowl, cover with plastic wrap or a towel, and let rise in a warm draft-free area until doubled in bulk, approximately 1 to 1½ hours.
05 - While dough rises, blend brown sugar, cinnamon, flour, and softened butter until a smooth spreadable paste forms.
06 - Punch down risen dough and roll into a 10×20 inch rectangle. Spread cinnamon filling evenly over surface, leaving a ½-inch border. Roll tightly from the long edge into a log.
07 - Pinch the seam to seal, then shape the log into an oval ring, connecting and pinching the ends securely. Transfer to a parchment-lined baking sheet.
08 - Cover loosely and let rise until noticeably puffy, about 45 minutes.
09 - Preheat oven to 350°F. Bake for 25–30 minutes until deep golden brown. Cool completely on a wire rack before icing.
10 - Whisk powdered sugar with milk and vanilla until smooth and pourable. Adjust consistency with additional milk if needed.
11 - Drizzle icing over cooled cake. Immediately sprinkle purple, green, and gold sanding sugars in alternating diagonal stripes while icing remains wet.
12 - If using the traditional plastic baby, insert it into the underside of the cooled cake before serving.