In a small bowl, combine the flour, baking soda, baking powder, cinnamon, nutmeg, cardamom, and ginger. Set aside.
Cream the softened butter with sugar in a large bowl using a hand mixer. Slowly add the eggs and milk until combined well. Stir in the diced apples using a spatula.
Gradually add the flour mixture until fully combined using the spatula. The mixture will be very sticky.
Dust flour onto a clean surface and generously dust flour on all sides of the dough. Work flour into the dough until it is no longer sticky, becomes soft and is easy to work with.
Flatten the dough to about an inch with your hands or a rolling pin. Use a doughnut cutter to cut out the doughnuts.
Transfer the cut doughnuts to a parchment-lined sheet pan for easy transport to the fryer later. Collect the scraps, rolling and cutting them again until all dough is used. Any small scraps can be turned into doughnut holes.
Heat at least 2 inches of oil in a heavy-bottomed pot or deep fryer to 380 degrees. A candy thermometer helps monitor the temperature and adjust accordingly. Using a slotted spoon, carefully transfer up to 4 doughnuts at a time (depending on the size of your pot) into the hot oil.
Don’t crowd the pan and watch the temperature. The oil will cool quickly once you add the doughnuts. Ideally, keep the oil between 365-385 degrees.
Allow the doughnuts to fry for 2 minutes on each side. Use a long-handled spoon and carefully flip the doughnuts to maintain even browning. Total frying time is 4 minutes.
Remove from the hot oil and rest on a wire rack to allow the oil to drain. Continue working in batches until all doughnuts are fried. Once the doughnuts are cool enough to touch, drizzle with or dip into the spiced glaze. Decorate if you’d like with sprinkles or diced fresh apple. Let them rest for about 10 minutes for the glaze to set before digging in.