Feed your starter: Make sure your sourdough starter is active and bubbly. In a bowl, combine the starter, warmed milk, and eggs. Whisk until smooth.

Mix dry ingredients: In a large mixing bowl, whisk together the flour, sugar, salt, and cinnamon. Grate in the orange zest if using.

Form the dough: Add the wet ingredients to the dry, mixing until a shaggy dough forms. Knead for about 8–10 minutes until the dough is smooth and slightly elastic.

First rise: Place the dough in a lightly oiled bowl, cover, and let it rest at room temperature for 3–4 hours, or refrigerate overnight.

Prepare the filling: Mix brown sugar, cinnamon, and melted butter in a small bowl.

Shape the cake: Divide the dough into three equal pieces and roll into long ropes. Braid loosely and seal the ends to create a ring.

Second rise: Cover the braided ring and let it proof for 1–2 hours. Preheat the oven to 375°F (190°C) during the last 20 minutes.

Brush the braid lightly with beaten egg and bake for 25–30 minutes until golden and hollow-sounding.

Glaze and decorate: Let the cake cool, whisk the powdered sugar glaze until smooth, and drizzle over the cake. Sprinkle colored sanding sugar in festive stripes.

If hiding a trinket, insert it before the first slice. Serve warm and enjoy.