Throw butter in the freezer 15-20 min before starting.
Add all the dry ingredients to a medium-sized mixing bowl, mix well.
Shred the butter with a cheese grater using the finest grate.
Mix it in with the dry ingredients.
Add milk and slightly mix everything until it is cohesive. Do not over-stir.
Lightly spread a thin layer of flour on the countertop.
Transfer dough to the countertop.
Work the dough out flat with your hands, fold over and flatten out again. Repeat several times until the dough holds together well.
Flatten the dough out about 1/2" thick. Next, cut out Donuts using a cookie cutter or the rim of a cup. Then, use your thumb to punch out the center hole.
In a cast iron skillet over medium heat with about an inch of oil, add in the donuts. Be careful not to splash out the hot oil.
Fry for about 1-2 minutes, then flip with tongs and fry for an additional 1-2 minutes.
In a small shallow dish, mix the sugar and cinnamon. Dip donuts immediately into the mixture while still hot.
Notes
Be very careful when frying these, as hot oil will splatter.
Leave a little room between the donuts since they will expand as they are heated.
Shaping your donuts: An alternative to steps 6-9, you can divide the dough up, roll it into small balls, flatten it, and then poke the hole out in the middle.