Preheat the oven to 350 F (177C). Spray a regular-size 6-donut pan with nonstick spray. You can also make these in a regular-size muffin pan, which will yield 8 muffins.
Add the flour, cornstarch, pumpkin pie spice, baking powder, and salt to a large bowl, and whisk well.
To the same bowl, add the syrup, pumpkin, yogurt, and chocolate chips. Stir the ingredients well until a smooth batter is formed. The batter will be on the thick side. Be careful not to overmix.
Spoon the batter evenly into the prepared pan. Using the back of a spoon, smooth and flatten out the tops of each donut. If you don't do this, they will bake up really lumpy and ugly. If you're making muffins, I find using an ice-cream scoop gives a nice rounded top.
Bake at 350F for 15 minutes or until the donuts have risen beautifully, are fluffy, have a golden-brown top, and lightly spring back when touched. Muffins may take closer to 20 minutes. Look for a clean toothpick when it's inserted in the center.
Let the donuts cool in the pan for about 5 minutes and then carefully flip them over onto a cooling rack. Let them cool completely. Once cooled, store any extras in a large, sealed container or ziplock bag so they don't dry out.
If you are making the Pumpkin Spice Sugar, simply mix both ingredients in a small bowl. You can spray the donuts with a light coat of the spray you used for the pan, or even spray water. Then sprinkle with sugar and it should stick pretty well.
If you are making the Chocolate Pumpkin Sauce, slowly melt the chocolate chips in the microwave or on the stove. Once melted stir in the pumpkin and dash of salt and mix well. Dip the pumpkin in or coat them with the sauce.