Bloom the yeast. In a large bowl, combine warm milk, a pinch of sugar, and yeast. Let it sit until foamy, about 5–10 minutes. If it doesn’t foam, start over with fresh yeast.

Mix the dough. Whisk in the remaining sugar, melted butter, eggs, and vanilla. In a separate bowl, combine 3 cups flour, salt, nutmeg, and lemon zest. Add dry ingredients to the wet mixture and stir until a shaggy dough forms.

Knead until smooth. Turn the dough onto a lightly floured surface. Knead 6–8 minutes, adding small amounts of flour as needed, until the dough is soft, elastic, and slightly tacky but not sticky.

First rise. Place the dough in a greased bowl, cover, and let rise in a warm spot until doubled, about 1–1 1/2 hours.

Prepare the filling. Mix softened butter, brown sugar, cinnamon, and a pinch of salt into a spreadable paste.

Shape the cake. Punch down the dough and roll it into a 10x18-inch rectangle. Spread the filling evenly, leaving a 1/2-inch border. Roll up from the long side into a tight log. Pinch the seam to seal.

Form the ring. Transfer the log to a parchment-lined baking sheet. Shape it into a circle and pinch the ends together firmly. Make 8–10 shallow diagonal slashes around the ring to help it expand evenly.

Second rise. Cover loosely and let rise until puffy, 30–45 minutes. Meanwhile, preheat the oven to 350°F (175°C).

Bake. Bake for 25–30 minutes until golden brown and set. If it’s browning too fast, tent loosely with foil for the last 5–10 minutes. Let cool completely on a rack.

Hide the baby. Once cool, gently insert the plastic baby or dried bean into the bottom of the cake. Never bake plastic inside the cake.

Glaze and decorate. Whisk powdered sugar, milk (or lemon juice), and vanilla into a thick but pourable glaze. Drizzle over the cooled cake. Immediately sprinkle stripes of purple, green, and gold sugar while the glaze is still wet.