1. Combine Wet Ingredients for the Dough: In a large mixing bowl, whisk together the active sourdough starter, warm milk, granulated sugar, beaten egg, and vanilla extract until well combined. The mixture should look slightly milky and have a few bubbles from the active starter.

2. Mix Dry Ingredients and Form Dough: In a separate bowl, whisk together the 4 cups of all-purpose flour, ground cinnamon, ground nutmeg, ground cloves, and salt. Gradually add the dry ingredients to the wet ingredients, mixing with a wooden spoon or your hands until a shaggy dough forms.

3. Knead in Butter and Fruit: Turn the dough out onto a lightly floured surface. Knead the dough for about 5 minutes until it starts to come together. Then, gradually knead in the softened butter, a tablespoon at a time, until it’s fully incorporated and the dough is smooth and elastic (about 5-7 more minutes). Finally, knead in the dried currants or raisins until they are evenly distributed. The dough should feel soft and slightly tacky, but not overly sticky.

4. First Rise (Bulk Fermentation): Place the dough in a lightly oiled bowl, turning it once to coat. Cover the bowl with plastic wrap or a clean kitchen towel and let it rise in a warm place for 4-6 hours, or until doubled in size. Alternatively, you can place it in the refrigerator overnight (8-12 hours) for a slower, more flavorful rise.

5. Shape the Buns and Second Rise: Gently punch down the risen dough and turn it out onto a lightly floured surface. Divide the dough into 12 equal pieces. Shape each piece into a smooth, round bun. Arrange the buns in a greased 9×13 inch baking dish, leaving a little space between them. Cover the dish and let the buns rise again in a warm place for 1-2 hours, or until they look puffy and almost doubled in size.

6. Prepare and Pipe the Crosses: Preheat your oven to 375 F (190 C). While the oven heats, prepare the cross mixture: In a small bowl, whisk together the 1/2 cup all-purpose flour with 3-4 tablespoons of water until you have a thick, pipeable paste. Transfer the paste to a small piping bag or a Ziploc bag with a tiny corner snipped off. Carefully pipe a cross onto the top of each risen bun.

7. Bake the Buns: Bake for 20-25 minutes, or until the buns are golden brown on top and sound hollow when tapped on the bottom. Keep an eye on them to prevent over-browning.

8. Glaze and Serve: While the buns are still warm, prepare the glaze. Whisk together the powdered sugar and milk or water until smooth. Drizzle or brush the glaze generously over the warm hot cross buns. Serve immediately and enjoy!