Dissolve yeast in warm water in a medium bowl, let rest for 10 minutes.
Add milk, sugar, salt, eggs, shortening or butter, and 2 cups flour.
Beat on low for 30 seconds, scraping bowl constantly. Beat on medium speed for 2 minutes, scraping bowl occasionally. Stir in remaining flour until smooth.
Cover and let rise until double, 45-90 minutes. (Dough is ready when indentation remains when touched.)
Turn dough onto floured surface; roll around lightly to coat with flour. Gently roll dough 1/2-inch thick with floured rolling pin.
Cut with floured doughnut cutter.
Place cut donuts on a parchment or baking mat lined baking sheet. Cover and let rise until double, 20-30 minutes.
While the cut doughnuts rise, make the creamy glaze - heat butter until melted. Remove from heat. Stir in powdered sugar and vanilla until smooth. Stir in water, 1 tablespoon at a time, until desired consistency.
Heat vegetable oil in deep cast iron skillet to 355 to 365 degrees F (use a thermometer here, it makes all the difference!).
Slide doughnuts into hot oil with wide spatula. Turn doughnuts as they rise to the surface. Fry until golden brown, about 1 minute on each side.
Remove carefully from oil; drain on a double layer of paper towels.
Dip the hot doughnuts into creamy glaze, then set on cooling rack set inside of a rimmed baking sheet to collect the drips.
Best enjoyed warm with friends.
Notes
The dough should be very soft but not overly sticky. It's ok if it's a bit tacky, but if it's sticking to your hands and won't come off, you need a bit more flour.
To scald the milk I just stick it in the microwave and get it nice and hot. But be sure to let it come down to around 110 degrees F. If you add the milk to your yeast mixture while the milk is too hot you can kill your yeast which will ruin the recipe.
Don't have a donut cutter? I LOVE these biscuit cutters and the largest one with the smallest one as the hole works great for this recipe.
If you don't love glaze, these donuts are also great rolled in cinnamon sugar or powdered sugar.