Punch the dough down to remove excess air. Transfer the dough to a clean and lightly floured surface, then roll it out to a 12″ x 16″ (30 x 40 cm) rectangle. If the dough keeps springing back a lot while rolling it out, let it rest for 5 minutes before
Spread the melted butter over the dough, then sprinkle the cinnamon sugar over the butter in an even layer.
From the longer side, fold the dough in half. Cut the dough into 6 strips that are ~2" wide and ~8" long.
Cut each strip in half long-ways, leaving the strip still attached at the top. Twist the two strips together, then make a circle with the twisted dough and bring one end of the strip through the circle and gently pull on it to make a knot.
Cut out 6 parchment squares that are ~4". Transfer the dough balls each to their own parchment square, then cover them loosely with a towel. Allow them to rise in a warm environment for ~30 minutes, or until they have slightly puffed up.
Once the donuts have puffed up, fill a large saucepan with at least 2" of vegetable or any neutral oil. Heat the mixture to 350°F / 175°C.
Carefully place the donuts in to the fryer with the parchment paper (2-3 at a time, depending on what your pan can fit). After ~5-10 seconds, remove carefully remove the parchment from the donuts using metal tongs.
Fry the donuts on each side for 2-3 minutes, or until they are a deep golden brown. You can also check if they are done by making sure the internal temperature is at least 190°F / 87°C.
Remove the donuts from the oil with a metal slotted spoon and set them on a wire rack to cool.