In a medium bowl combine flour, spices, baking powder and salt.
In a stand mixer combine shortening and sugar. Mix a until combined.
Add egg yolks and mix until light yellow and fluffy.
Add the dry ingredients and the sour cream to the wet ingredients, 1/3 at a time. Alternate between dry ingredients and sour cream. Mix after each addition.
Cover with plastic wrap and refrigerate at least 45 min, up to overnight. Dough will be sticky.
Turn out on well floured surface. Roll to 1/2 inch thick. Cut with donut cutter.
Make Glaze before frying (see below)
Fry at 325F. Add donuts to hot oil and fry for 10 seconds. Flip over gently and then fry for 75-90 seconds on one side, flip over and fry an additional 75 seconds on second side.
Remove to a paper towel lined plate.
Dunk hot donuts into glaze.
Glaze
Mix all ingredients together with a whisk. Dunk donuts while still hot.