Preheat oil in either a large Dutch oven or deep-fryer to about 365 degrees F.
In a large bowl mix together flour, salt and baking powder. In a small bowl, using a hand mixer, beat the shortening and sugar together until light and fluffy. Add in the egg and vanilla extract. Combine the lemon juice and the milk together in a small bowl, and add to the egg mixture. Stir in the flour mixture and combine well to create the doughnut batter. Allow to rest for 5 minutes.
Roll the dough out on a floured surface to about 1 to 2-inch thickness. Using a 2 1/2-inch pastry cutter, cut out doughnuts. Allow to rest for another 5 minutes, then fry in hot oil, in batches, until golden brown. Remove from the oil and drain on paper towels. Coat with cinnamon-sugar and place on a serving platter.