In a medium sized bowl, whisk to combine the flour, baking powder, salt, cinnamon and nutmeg. Set aside.
In the bowl of an electric mixer, beat the butter and sugar together until well combined. With the mixer running, add the vanilla and the egg yolks. Turn the mixer to low and add the sour cream. Use a spatula to stir in the dry ingredients until just combined.
Cover the bowl with plastic wrap and refrigerate for one hour. While the dough chills, mix the glaze together.
Once chilled, turn the dough out onto a lightly floured surface. Fold the dough over on itself to smooth it out a little. Use a rolling pin to roll the dough into 1/2 inch thickness. Dip your donut cutter in a small bowl of flour to prevent sticking and cut out as many donuts as possible. Reroll out dough if needed. Place donuts on a parchment lined baking tray and place tray in the fridge to chill donuts for at least 15 minutes.
While donuts chill, gather what you need for frying. Line a plate with paper towels. Take out a spider strainer and/or tongs.
Fill a Dutch oven with about 3 inches of oil. Attach a candy thermometer to the edge. Make sure the thermometer doesn't touch the bottom. Heat oil to 345-360 degrees F.
Use tongs to carefully place 3 donuts in the hot oil. Fry for 1 to 1½ minutes per side until donuts are golden brown. Donut holes will take up to 1 minute to fry. Transfer donuts to paper towel lined plate to cool slightly.
Check the temperature of the oil again. Adjust heat so that the oil stays within 345 and 360 degrees F. Continue frying the remaining donuts and donut holes.
Allow donuts to cool for 5 minutes then dip warm donuts in the glaze. (If the glaze has hardened a bit, just pop it in the microwave for about ten seconds then stir to smooth it out). Place donuts on a cooling rack to allow the glaze to slight slightly. Enjoy while still warm or once cooled!