In the bowl of a stand mixer fitted with the paddle attachment, add the yeast*, 1/2 cup warm milk, honey, egg whites and 1 1/4 cups of the flour. Reserve the additional 1 cup for later. Beat on medium-high for about 3 minutes, or until the mixture is smooth and light, but thick.

Remove the paddle, and scrape down the sides of the bowl. Sprinkle the remaining 1 cup of flour on top of the mixture, but DO NOT STIR. Cover with a tea towel and place the bowl in a warm location and let it sit for about 30-40 minutes, or until the yeasted mixture has started to bubble through the flour that was sprinkled on top.

Return the bowl to the stand mixer, and attach the dough hook. Add the egg yolks, vanilla, salt and remaining 2 tbsp of milk and mix on low until a shaggy dough forms. Increase the speed to medium and beat for 8-10 minutes, or until the dough is soft and smooth. It should clear the sides of the bowl, but stick slightly to the bottom.

Reduce mixer speed to medium-low, and add one piece of butter at a time, letting the dough and butter fully combine before adding more. This process can take some time, so be patient. The dough should be very smooth and slightly tacky once all the butter has been incorporated.

Cover and chill in the fridge for at least 8 hours, or up to 16 hours.

Melt the butter, and stir in all remaining ingredients. Mix well and set aside to cool.

Punch the dough down and turn it out a lightly floured work surface. Roll the dough out into a rectangle about 16x12 inches.

Spread the filling mixture over the dough, making sure the longest side of the dough is closest to you, then roll the dough up like you would with a regular cinnamon roll. Place the roll seam-side down on a cutting board, or other transportable flat surface, cover with plastic wrap, and place in the fridge to chill for at least 20 minutes.

Preheat the oven to 350 degrees F. Grease a 12-cup muffin tin and set aside.

Once chilled, remove the dough from the fridge, and trim about 1/2 inch from each side. Cut the log into 12 equal pieces. Place each piece, cut side up, into the prepared muffin tin. Cover loosely with plastic and allow to rise for another 15 minutes, or until the dough has puffed up to the edges.

Bake the buns for 20-25 minutes, or until golden brown all over.

Meanwhile, heat 2 tbsp of butter and 2 tbsp of honey in a small saucepan over low heat. Set aside.

Remove the buns from the oven, and brush the tops with the butter and honey mixture. Sprinkle with coarse sugar and transfer to a cooling rack immediately. Best if eaten warm. Buns keep in an airtight container for up to 5 days.