Make sure your sourdough starter is active and bubbly.
In a large bowl or the bowl of a stand mixer, mix the sourdough starter, warm milk, and sugar until dissolved. Add the flour, softened butter, egg, vanilla extract, spices, and salt. Mix until a rough dough forms.
Meanwhile, soak the raisins in the orange zest and juice for 2–3 minutes.
Add the raisins and juice to the bowl with the dough. Turn the mixer on medium speed and mix for 4-5 minutes until a smooth dough forms. You can also knead the dough by hand for 6-8 minutes on a lightly floured surface.
Cover the dough with a damp cloth and let it rise at room temperature for 10-12 hours, or until it doubles in size. Don’t rush it, good things take time! If your kitchen is cold, this might take up to 12 hours to rise. It is most important that it doubles in size. Overnight is a great option.
After the dough has doubled in size, punch down the dough and divide it into 12 equal pieces. Roll each piece into a smooth ball and put them into a greased baking dish, leaving a little space between them.
Cover and let the buns proof for 1-2 hours at room temperature. They should puff up nicely and start to touch each other.
Mix the flour and water into a paste, then pipe a cross onto each bun using a piping bag or a zip-top bag with the corner snipped.
Preheat your oven to 375 degrees F. Bake the buns for 35-40 minutes until they’re golden brown.
While the buns are baking, heat the apricot jam and water together until smooth. When the buns are done baking, brush this glossy mixture over the warm buns for that perfect finish.
Let the buns cool slightly before serving. They’re best fresh out of the oven.