In a larger bowl, combine the flour and salt, cinnamon and sugar.
In a glass container, heat water and use a thermometer to make sure it is at the proper temperature. Add yeast, stir to combine, cover and allow to activate for 10 minutes.
Pour activated yeast into the dry ingredients. Use a spoon to mix together. Cover and set aside for 1-18 hours to allow it to rise before you are ready to prepare the oil for frying and making the frittelle.
When the dough is ready, dust a flat surface with a little flour, and bring the dough into a ball. You'll want to keep your ball of dough covered in-between cutting and frying, so that it will not be compromised or dry out.
Pour oil into a wide-bottom pot, set to medium-high heat and heat the oil to between 360-375 degrees Fahrenheit or 182-190 degrees Celsius. Get everything you need ready to go for frying. I recommend tongs, a pastry cutter, sugar ready in a bowl, a cooling rack and towel to blot oil from fresh-fried frittelle.
Cut the dough into pieces. For plain rustic-style fry bread/donuts, you can stretch out the pieces a bit and set them aside. If you like, puncture a hole in the center.
For filled frittelle: Stretch the dough flat without any holes, and place it onto a surface. Fill the center with enough filling so that it can be closed completely without any holes.
Fold the dough over. Use your fingers to seal it.
Make sure your piece is closed. If holes happen during frying, it is ok. It's just that moisture will go into the hot oil and it could spray up or make a mess. It's not the worst thing and it will not totally ruin the frittelle.
Once the oil has come to the proper temperature: place 3-5 pieces inside the hot and prepared oil, so that they do not touch, and there is no overcrowding. You'll allow them to turn slightly golden brown before flipping. You'll notice they will float and turn a golden brown and you'll keep turning them - 2-4 times each side. You will know when because of how they look and feel when you use the tongs to turn them. Once perfectly golden, remove from the oil and set onto a cooling rack with paper or reusable cloth. Plain and center-hole frittelle will cook the fastest - about 3-5 minutes, depending on the size of your dough. Filled frittelle take longer to cook completely on the inside and on the outside. Keep and eye on them and because you are trying to avoid puncturing them, you want one side to set or be truly golden before flipping. Filled frittelle will take a couple minutes longer than plain to fry. For sugar-topped frittelle, you'll take them strait from the cooling rack, and into a bowl with the sugar.
Coat both sides and serve.
An option is to drizzle or dip with apple-pie reduction-glaze.