In a small bowl, sprinkle yeast over milk. Let sit for a minute, then stir to combine. Let sit until frothy.

In the bowl of a large food processor fitted with a dough blade or a large bowl, combine flour, sugar, and salt. Mix in the yeast with milk, butter, and egg yolk until dough comes together. Process or knead on lightly floured surface until smooth and elastic. Place in large oiled bowl, cover, and let rise until doubled, about 1 hour.

Line a large baking sheet with parchment.

In a small bowl, combine filling ingredients: butter, sugar, and cinnamon.

On a floured surface, divide the dough into 8 equal pieces. Roll a piece into a 5 inch wide circle. Use a pastry brush to spread filling over the circle in a thin layer. Roll the circle up. Cut down the middle lengthwise, leaving about 1/8 inch intact at the edge. Twist the two pieces together, fanning the cut side outward. Seal the edges together to form a circle. Place on prepared baking sheet. Repeat with remaining pieces. Cover and let rise until puffy, about 30 minutes. Preheat oven to 395 degrees F.

If desired, brush the tops with remaining filling. Bake in preheated oven for 5 minutes, then reduce heat to 345 degrees Bake until golden brown, 10-12 minutes.

If desired, top with powdered sugar before serving.