Step 1

In a medium bowl, mix the starter, milk, and flour together to form a stiff dough. Cover the bowl and ferment the levain at room temperature until more than doubled in volume, puffy, and domed, about 8 to 12 hours.

Step 2

In the bowl of a stand mixer fitted with the dough hook, mix together the flours, sugar, milk powder, egg, milk, cream, and levain until just combined. Cover and autolyse (rest) for 45 minutes.

Step 3

Add the salt and knead on medium-low speed until the gluten is moderately developed, about 5 minutes. The dough will start out sticky and rough but should gradually come together and feel quite smooth and stretchy. Turn the mixer to low and add the butter about 1 tablespoon at a time, incorporating each batch before adding the next. Turn the speed back up to medium-low and continue kneading until the gluten is very well developed and the dough passes the windowpane test, about 10 to 15 minutes. The dough should be smooth and supple.

Step 4

Shape the dough into a smooth ball and transfer to a lightly oiled container. Cover and let rise at room temperature for 2 hours. The dough will be noticeably expanded but not doubled. Stretch and fold the dough (see page 108), cover, and refrigerate for at least 8 hours and up to 24 hours.

Step 5

When ready to shape, in a small bowl, cream together the butter, sugar, cinnamon, and salt to form a spreadable paste. Lightly grease a 9 x 9–inch (23 x 23–cm) baking pan or a 9- or 10-inch (23- or 25-cm) round cake pan (preferably aluminum). Take the dough out of the fridge and transfer to a lightly floured surface. Roll into a 14-inch (36-cm) square, doing your best to maintain an even thickness.

Step 6

Spread the filling mixture evenly over the dough, going all the way to the edges.

Step 7

Roll the dough up like a jelly roll, pinching to seal. Turn the roll so the seam side is down.

Step 8

Baker's NotesFor extra gooey rolls, use this trick from Sarah Kieffer of the Vanilla Bean Blog: Spread a small amount of frosting over the rolls as soon as they come out of the oven. Let cool, then spread on the remaining frosting.These rolls keep well for 2 to 3 days in a sealed plastic bag. Reheat briefly in the microwave to refresh, and wait until just before eating to frost.