In a large bowl, mix the yeast with the milk, eggs, granulated sugar, and cinnamon. Add the flour, sprinkle the salt on top, and mix with a stiff spatula or einkorn dough spoon to combine. Add the butter and mix until smooth.
Cover the bowl tightly with plastic wrap and let rest for 60 minutes.
Heavily dust a 20-inch-long piece of parchment paper with flour. Transfer the dough to the paper and roll the dough to a 12 × 18-inch rectangle.
Make the Filling:
In a small bowl, mix together the brown sugar, flour, cinnamon, and salt. Mix in the butter. Spread the mixture over the rectangle of dough reaching all the way to the sides. Roll the dough across its width to form a long, fairly tight cylinder.
Cut the dough into ten 2-inch-thick rounds and place cut side down in a buttered 9-inch cake pan. Cover with plastic wrap and let rest for 30 minutes.
Preheat the oven to 375°F.
Bake the rolls for 23 to 25 minutes until evenly golden and firm. Let cool for 10 minutes on the baking sheet or cake pans. Lift with a metal spatula or invert the cake pans onto a wire rack to cool for 15 minutes before glazing.
Make the Glaze:
Combine the powdered sugar and water in a small bowl. Drizzle the glaze in strips over the buns. Serve warm. The buns can be stored, tightly wrapped, at room temperature for up to 3 days.
Notes: If you would like to make these with sourdough, replace the yeast with ¼ cup (60 g) of sourdough starter, and let them rise overnight or 8 to 10 hours. Increase the second proofing time to 2 hours.