Pour the milk into the bowl of a stand mixer fitted with the beater attachment and sprinkle the yeast on top. Add the eggs, egg yolk, butter, and sugar, beating to combine.

Add the salt and four cups flour and beat until just barely combined. Let sit for five minutes so the flour can soak up the liquids. Remove the beater attachment and attach the dough hook.

Knead the dough on medium speed for five to seven minutes, adding up to 1/2 cup more flour if needed to bring the dough together. It should be elastic and smooth, but it will also be tacky and will stick to the sides of the bowl.

Spray a large bowl with cooking spray. Use a rubber spatula to transfer the dough from the mixer bowl to the greased bowl. Cover with a kitchen towel or wax paper and place in a warm spot to rise until doubled. (To do this in the oven, turn the oven to the lowest setting for one to two minutes, then turn it off and let the dough rise inside, uncovered, for about 30 minutes. Do not allow the dough to rise too much or the cinnamon rolls will be airy.)

Preheat the oven to 350 degrees Fahrenheit.

Prepare the filling: In a medium bowl, combine the butter, sugar, salt, and cinnamon. Set aside.

Sprinkle a baking mat generously with flour. Cut the dough into four pieces. Working with one piece at a time, place on the mat and sprinkle with flour. Flour a rolling pin and roll the dough into a 9×13-inch rectangle.

Use a rubber spatula to spread the filling over the dough. Starting at one long side, roll up the dough jelly-roll style. Cut into 20 pieces.

Place six pieces in each baking tin. Pour 1/4 cup heavy cream over the pieces in each tin and bake for 18 to 20 minutes.

Prepare the glaze: In a bowl, whisk together the confectioners’ sugar and milk until smooth. Add the sour cream and whisk until smooth and creamy. Set aside.

Prepare the frosting: Cream together the cream cheese and butter until fluffy. Add the confectioners’ sugar and beat until smooth. Stir in the maple syrup and cinnamon. Transfer to a piping bag fitted with a round tip.

Trim the end of each swirl to get one flatter side of each bun. Drizzle with glaze and pipe frosting on top. Stack four buns together.

Put four stacks into each container. Drizzle more glaze on top of the frosting and garnish with hazelnut brittle.

To assemble the large buns, follow the same steps. Put one stack in each box.