In a mixing bowl fitted with a dough hook attachment, combine flour, sugar, salt, and yeast.

Add milk, eggs, sourdough starter, and vanilla extract. Mix 5 minutes on medium speed.

Add 295 grams butter and mix additional 10 minutes, or until dough is smooth and elastic.

Transfer dough to a greased, nonreactive container. Cover and refrigerate overnight.

On a work surface, roll out remaining 454 grams butter into a 12-inch square. Wrap butter in plastic wrap and refrigerate overnight.

The next day, on a lightly floured work surface, roll dough into a 12-inch by 24-inch rectangle.

Place butter square on one half of the dough rectangle. Fold the other half over and seal edges.

Roll dough into a long rectangle, then fold into thirds. Refrigerate 30 minutes.

Repeat process additional two times, making sure to chill 30 minutes between each fold. Cover dough and refrigerate.

In a food processor, pulse to combine all ingredients for Anise-Citrus Sugar. Transfer to an airtight container and reserve.

Remove Brioche from refrigerator. Let sit 15 minutes at room temperature.

On a lightly floured work surface, roll Brioche into an 11-inch by 18-inch rectangle.

Brush with melted butter. Sprinkle with Anise-Citrus Sugar.

Starting from the bottom, roll Brioche upwards into an 18-inch log. Slice into nine 2-inch rolls.

Transfer rolls, swirl-side-up, into greased muffin tins. Let sit 3 hours at room temperature, or until puffed up.

In a mixing bowl, combine all ingredients for Orange Blossom Glaze. Transfer to a mixing bowl and set aside.

Heat oven to 425°F. Bake Buns 20 minutes. Reduce heat to 350°F. Rotate tins and make additional 40 minutes.

Transfer Buns to wire rack and let cool. Once cooled, dip into Orange Blossom Glaze.