This is a certain holiday show-stopper, with its beautiful rippled golden dough and deliciously nutty and floral pistachio fragrance. And with all that, it tastes as good as it looks!
For the bread dough, whisk together the yeast and milk in a small bowl and allow to sit at room temperature until yeast is dissolved, about 5 minutes.
In the bowl of a stand mixer fitted with the dough hook attachment, combine the flour, 1/2 cup of water, butter, vanilla extract, sugar, salt, and yeast mixture at low speed until the dough comes together. If it seems dry and crumbly, add up to 4 tablespoons more water. Continue mixing until a soft smooth dough forms. You can do this by hand, as well, and just knead the dough. Transfer the dough to a greased bowl, cover, and let it rise for 60 minutes at room temperature out of direct sunlight.
On a clean and lightly floured working surface, divide the dough into four equal parts and pat into rough square shapes (when I made this the bread dough weighed 22 ounces, so I used a kitchen scale to divide into 4 separate 5.5 ounce pieces). Cover and refrigerate for 30 minutes.
While the dough is in the refrigerator, prepare the pistachio filling by pureeing together the butter, sugar, pistachios, salt, vanilla extract, and cinnamon in a blender or food processor until relatively smooth and the pistachios nuts have released their oils (it will be very fragrant). Set aside.
Take one of the dough squares and roll it out on a piece of parchment paper into a roughly 9-inch square. Spread the surface with 1/3 of the pistachio mixture, leaving an empty 1-inch border around the edges, then set it aside.
Take a second dough square and roll it out onto a piece of parchment paper, then flip it upside down on top of the first sheet of dough, peeling off the top layer of parchment paper and pressing around the edges gently to seal the two layers of dough together. Spread another 1/3 of the pistachio mixture onto the top layer of dough, leaving an empty 1-inch border around the edges, then repeat this process one more time so that you have three layers of buttered dough stacked on top of each other. (You can refer to the above video for the assembly steps).
Roll out the fourth and final dough square onto a piece of parchment paper, then flip it upside down on top of the third sheet of dough, peeling off the top layer of parchment paper and pressing around the edges gently to seal the two layers of dough together. (This top layer does *not and will not* have any pistachio mixture on top of it.)
Place a 2" lid of a jar in the center of the circle as a guide, and cut the circle into 16 equally-sized slices, leaving the center 2" connected. Twist the slices in pairs away from each other. Then pinch the ends of each pair together. Set the star aside to rise for 30 minutes at room temperature out of direct sunlight.