There is nothing better than tender and tasty homemade cake donuts.

In a large bowl or the bowl of a stand mixer, cream the butter. Gradually stir in brown sugar and beat until smooth for 1 minute. Stir in the eggs one at a time. Add the vanilla and beat on high speed for 2 minutes.
In another large bowl, combine the flour, baking powder, salt and cinnamon. At low speed, gradually incorporate the dry ingredients, alternating with the milk. At this stage you have to beat until homogeneous not more.
On a lightly floured surface, using a rolling pin, roll out one-third of the dough to ½ inch thick. Cut the dough using a floured donut cutter and place the donuts on lightly floured baking sheets spacing them as you go. Repeat this operation with the rest of the dough.

Place sheets of absorbent paper on cookie sheets to place the fried donuts.
About 15 minutes before frying, in a deep casserole or better in a deep fryer, heat 4 inches of oil to 375 ° F. Constantly monitor the heat of the oil and do not get distracted from pan for any reason.
Fry about 3 donuts at a time for 2 minutes. Turn and cook for about 2 minutes. Drain and place on the plates. (To check if donut is cooked through, cut one donut in half at the beginning of frying. If the donut has uncooked dough in the center and is brown on the exterior this means the oil is too hot). Finish with the donut holes.
Donuts are at the best the day they are cooked and can be frozen for 3 months.