I used to be the Executive Chef at the JCC of Manhattan ( Jewish Community Center) I made 1000's of jelly donuts. This recipe works well and always had people sneaking into the kitchen and stealing dozens to take home.
1 scant tablespoon (1 package) dry yeast
4 tablespoons sugar
3/4 cup lukewarm milk or warm water*
2 1/2 cups all-purpose flour
Pinch of salt
1 teaspoon ground cinnamon
2 eggs, separated
2 tablespoons (1/4 stick) butter or pareve margarine, softened*
Apricot or strawberry preserves or whatever you want
Sugar
Vegetable oil for deep-frying
*Use butter and milk if serving at a milk meal, and water and pareve margarine for a meat meal
Preparation
Mix together the yeast, 2 tablespoons of the sugar, and the milk. Let sit to make sure it bubbles.
Sift the flour and mix it with the remaining sugar, salt, cinnamon, egg yolks, and the yeast mixture.
Knead the dough until it forms a ball. Add the butter or margarine. Knead some more, until the butter is well absorbed. Cover with a towel and let rise overnight in the refrigerator.
Roll out the dough to a thickness of 1/8 inch.
Cut out the dough into 24 rounds with a juice glass, or any object about 2 inches in diameter. Take 1/2 teaspoon of preserves and place in center of 12 rounds. Top with the other 12. Press down at edges, sealing with egg whites. Crimping with the thumb and second finger is best. Let rise for about 30 minutes.
Heat 2 inches of oil to about 375°. Drop the doughnuts into the hot oil, about 5 at a time. Turn to brown on both sides. Drain on paper towels.
Roll the doughnuts in sugar.